Merge tag 'v2.2.0' of github.com:OpenZeppelin/openzeppelin-solidity

v2.2.0

.github/PULL_REQUEST_TEMPLATE.md

@@ -16,6 +16,7 @@ Fixes #
     (https://github.com/OpenZeppelin/openzeppelin-solidity/blob/master/CONTRIBUTING.md),
   - added tests where applicable to test new functionality,
   - made sure that your contracts are well-documented,
-  - run the JS/Solidity linters and fixed any issues (`npm run lint:fix`), and
+  - run the Solidity linter (`npm run lint:sol`) and fixed any issues,
+  - run the JS linter and fixed any issues (`npm run lint:fix`), and
   - updated the changelog, if applicable.
 -->

.gitignore

@@ -32,10 +32,13 @@ npm-debug.log
 # truffle build directory
 build/
 
-# lol macs
-.DS_Store/
+# macOS
+.DS_Store
 
 # truffle
 .node-xmlhttprequest-*
 
 .zos.session
+
+# IntelliJ IDE
+.idea

.node-version

-v8.9.1

.travis.yml

@@ -25,11 +25,10 @@ jobs:
       name: "Unit tests"
       script: npm run test
 
-# solidity-coverage fails at parsing 0.5.x code
-#    - stage: tests
-#      name: "Unit tests with coverage report"
-#      script: npm run test
-#      env: SOLIDITY_COVERAGE=true
+    - stage: tests
+      name: "Unit tests with coverage report"
+      script: npm run test
+      env: SOLIDITY_COVERAGE=true
 
     - stage: tests
       name: "Unit tests using solc nightly"

CHANGELOG.md

 # Changelog
 
-## 2.2.0 (unreleased)
+## 2.2.0 (2019-03-14)
 
-## 2.1.2 (2019-17-01)
+### New features:
+ * `ERC20Snapshot`: create snapshots on demand of the token balances and total supply, to later retrieve and e.g. calculate dividends at a past time. ([#1617](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1617))
+ * `SafeERC20`: `ERC20` contracts with no return value (i.e. that revert on failure) are now supported. ([#1655](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/))
+ * `ERC20`: added internal `_approve(address owner, address spender, uint256 value)`, allowing derived contracts to set the allowance of arbitrary accounts. ([#1609](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1609))
+ * `ERC20Metadata`: added internal `_setTokenURI(string memory tokenURI)`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+ * `TimedCrowdsale`: added internal `_extendTime(uint256 newClosingTime)` as well as `TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime)` event allowing to extend the crowdsale, as long as it hasn't already closed.
+
+### Improvements:
+ * Upgraded the minimum compiler version to v0.5.2: this removes many Solidity warnings that were false positives. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+ * `ECDSA`: `recover` no longer accepts malleable signatures (those using upper-range values for `s`, or 0/1 for `v`). ([#1622](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1622))
+ * `ERC721`'s transfers are now more gas efficient due to removal of unnecessary `SafeMath` calls. ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+ * `Counter`'s API has been improved, and is now used by `ERC721` (though it is still in `drafts`). ([#1610](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1610))
+ * Fixed variable shadowing issues. ([#1606](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1606))
+
+### Bugfixes:
+ * (minor) `SafeERC20`: `safeApprove` wasn't properly checking for a zero allowance when attempting to set a non-zero allowance. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+### Breaking changes:
+ * `TokenMetadata` (in drafts) has been renamed to `ERC20Metadata`. ([#1618](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1618))
+
+## 2.1.3 (2019-02-26)
+ * Backported `SafeERC20.safeApprove` bugfix. ([#1647](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1647))
+
+## 2.1.2 (2019-01-17)
  * Removed most of the test suite from the npm package, except `PublicRole.behavior.js`, which may be useful to users testing their own `Roles`.
 
-## 2.1.1 (2019-04-01)
+## 2.1.1 (2019-01-04)
  * Version bump to avoid conflict in the npm registry.
 
-## 2.1.0 (2019-04-01)
+## 2.1.0 (2019-01-04)
 
 ### New features:
  * Now targeting the 0.5.x line of Solidity compilers. For 0.4.24 support, use version 2.0 of OpenZeppelin.

README.md

@@ -94,6 +94,24 @@ contract MyNFT is Initializable, ERC721Full, ERC721Mintable {
 }
 ```
 
+> You need an ethereum development framework for the above import statements to work! Check out these guides for [Truffle] or [Embark].
+
+On our site you will find a few [guides] to learn about the different parts of OpenZeppelin, as well as [documentation for the API][API docs]. Keep in mind that the API docs are work in progress, and don’t hesitate to ask questions in [our Slack][Slack].
+
+## Security
+
+OpenZeppelin the project is maintained by [Zeppelin] the company, and developed following our high standards for code quality and security. OpenZeppelin is meant to provide tested and community-audited code, but please use common sense when doing anything that deals with real money! We take no responsibility for your implementation decisions and any security problems you might experience.
+
+The core development principles and strategies that OpenZeppelin is based on include: security in depth, simple and modular code, clarity-driven naming conventions, comprehensive unit testing, pre-and-post-condition sanity checks, code consistency, and regular audits.
+
+The latest audit was done on October 2018 on version 2.0.0.
+
+Please report any security issues you find to security@openzeppelin.org.
+
+## Contribute
+
+OpenZeppelin exists thanks to its contributors. There are many ways you can participate and help build high quality software. Check out the [contribution guide]!
+
 ## License
 
 OpenZeppelin is released under the [MIT License](LICENSE).

RELEASING.md

@@ -51,12 +51,15 @@ git checkout release-vX.Y.Z
 git pull upstream
 ```
 
+Before starting the release process, make one final commit to CHANGELOG.md, including the date of the release.
+
 Change the version string in `package.json`, `package-lock.json` and `ethpm.json` removing the "-rc.R" suffix. Commit these changes and tag the commit as `vX.Y.Z`.
 
 ```
 git add package.json package-lock.json ethpm.json
 git commit -m "Release vX.Y.Z"
 git tag -a vX.Y.Z
+git push upstream release-vX.Y.Z
 git push upstream vX.Y.Z
 ```
 

contracts/access/Roles.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title Roles

contracts/access/roles/CapperRole.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../Roles.sol";

contracts/access/roles/MinterRole.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../Roles.sol";

contracts/access/roles/PauserRole.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../Roles.sol";

contracts/access/roles/SignerRole.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../Roles.sol";

contracts/access/roles/WhitelistAdminRole.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/access/roles/WhitelistedRole.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/crowdsale/Crowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../token/ERC20/IERC20.sol";
@@ -12,8 +12,8 @@ import "../utils/ReentrancyGuard.sol";
  * allowing investors to purchase tokens with ether. This contract implements
  * such functionality in its most fundamental form and can be extended to provide additional
  * functionality and/or custom behavior.
- * The external interface represents the basic interface for purchasing tokens, and conform
- * the base architecture for crowdsales. They are *not* intended to be modified / overridden.
+ * The external interface represents the basic interface for purchasing tokens, and conforms
+ * the base architecture for crowdsales. It is *not* intended to be modified / overridden.
  * The internal interface conforms the extensible and modifiable surface of crowdsales. Override
  * the methods to add functionality. Consider using 'super' where appropriate to concatenate
  * behavior.
@@ -66,7 +66,7 @@ contract Crowdsale is Initializable, ReentrancyGuard {
 
     /**
      * @dev fallback function ***DO NOT OVERRIDE***
-     * Note that other contracts will transfer fund with a base gas stipend
+     * Note that other contracts will transfer funds with a base gas stipend
      * of 2300, which is not enough to call buyTokens. Consider calling
      * buyTokens directly when purchasing tokens from a contract.
      */

contracts/crowdsale/distribution/FinalizableCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../math/SafeMath.sol";
@@ -6,7 +6,7 @@ import "../validation/TimedCrowdsale.sol";
 
 /**
  * @title FinalizableCrowdsale
- * @dev Extension of Crowdsale with a one-off finalization action, where one
+ * @dev Extension of TimedCrowdsale with a one-off finalization action, where one
  * can do extra work after finishing.
  */
 contract FinalizableCrowdsale is Initializable, TimedCrowdsale {

contracts/crowdsale/distribution/PostDeliveryCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../validation/TimedCrowdsale.sol";

contracts/crowdsale/distribution/RefundableCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../math/SafeMath.sol";
@@ -7,8 +7,8 @@ import "../../payment/escrow/RefundEscrow.sol";
 
 /**
  * @title RefundableCrowdsale
- * @dev Extension of Crowdsale contract that adds a funding goal, and the possibility of users getting a refund if goal
- * is not met.
+ * @dev Extension of FinalizableCrowdsale contract that adds a funding goal, and the possibility of users
+ * getting a refund if goal is not met.
  *
  * Deprecated, use RefundablePostDeliveryCrowdsale instead. Note that if you allow tokens to be traded before the goal
  * is met, then an attack is possible in which the attacker purchases tokens from the crowdsale and when they sees that

contracts/crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/crowdsale/emission/AllowanceCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../Crowdsale.sol";

contracts/crowdsale/emission/MintedCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../Crowdsale.sol";

contracts/crowdsale/price/IncreasingPriceCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../validation/TimedCrowdsale.sol";
@@ -31,7 +31,7 @@ contract IncreasingPriceCrowdsale is Initializable, TimedCrowdsale {
     }
 
     /**
-     * The base rate function is overridden to revert, since this crowdsale doens't use it, and
+     * The base rate function is overridden to revert, since this crowdsale doesn't use it, and
      * all calls to it are a mistake.
      */
     function rate() public view returns (uint256) {

contracts/crowdsale/validation/CappedCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../math/SafeMath.sol";

contracts/crowdsale/validation/IndividuallyCappedCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../math/SafeMath.sol";

contracts/crowdsale/validation/PausableCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/crowdsale/validation/TimedCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../math/SafeMath.sol";
@@ -15,6 +15,13 @@ contract TimedCrowdsale is Initializable, Crowdsale {
     uint256 private _closingTime;
 
     /**
+     * Event for crowdsale extending
+     * @param newClosingTime new closing time
+     * @param prevClosingTime old closing time
+     */
+    event TimedCrowdsaleExtended(uint256 prevClosingTime, uint256 newClosingTime);
+
+    /**
      * @dev Reverts if not in crowdsale time range.
      */
     modifier onlyWhileOpen {
@@ -82,5 +89,17 @@ contract TimedCrowdsale is Initializable, Crowdsale {
         super._preValidatePurchase(beneficiary, weiAmount);
     }
 
+    /**
+     * @dev Extend crowdsale
+     * @param newClosingTime Crowdsale closing time
+     */
+    function _extendTime(uint256 newClosingTime) internal {
+        require(!hasClosed());
+        require(newClosingTime > _closingTime);
+
+        emit TimedCrowdsaleExtended(_closingTime, newClosingTime);
+        _closingTime = newClosingTime;
+    }
+
     uint256[50] private ______gap;
 }

contracts/crowdsale/validation/WhitelistCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 import "../Crowdsale.sol";
 import "../../access/roles/WhitelistedRole.sol";
 

contracts/cryptography/ECDSA.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title Elliptic curve signature operations
@@ -14,16 +14,16 @@ library ECDSA {
      * @param signature bytes signature, the signature is generated using web3.eth.sign()
      */
     function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
-        bytes32 r;
-        bytes32 s;
-        uint8 v;
-
         // Check the signature length
         if (signature.length != 65) {
             return (address(0));
         }
 
         // Divide the signature in r, s and v variables
+        bytes32 r;
+        bytes32 s;
+        uint8 v;
+
         // ecrecover takes the signature parameters, and the only way to get them
         // currently is to use assembly.
         // solhint-disable-next-line no-inline-assembly
@@ -33,17 +33,25 @@ library ECDSA {
             v := byte(0, mload(add(signature, 0x60)))
         }
 
-        // Version of signature should be 27 or 28, but 0 and 1 are also possible versions
-        if (v < 27) {
-            v += 27;
+        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
+        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
+        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
+        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
+        //
+        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
+        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
+        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
+        // these malleable signatures as well.
+        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
+            return address(0);
         }
 
-        // If the version is correct return the signer address
         if (v != 27 && v != 28) {
-            return (address(0));
-        } else {
-            return ecrecover(hash, v, r, s);
+            return address(0);
         }
+
+        // If the signature is valid (and not malleable), return the signer address
+        return ecrecover(hash, v, r, s);
     }
 
     /**

contracts/cryptography/MerkleProof.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title MerkleProof

contracts/drafts/Counter.sol

-pragma solidity ^0.5.0;
-
-/**
- * @title Counter
- * @author Matt Condon (@shrugs)
- * @dev Provides an incrementing uint256 id acquired by the `Counter#next` getter.
- * Use this for issuing ERC721 ids or keeping track of request ids, anything you want, really.
- *
- * Include with `using Counter for Counter.Counter;`
- * @notice Does not allow an Id of 0, which is popularly used to signify a null state in solidity.
- * Does not protect from overflows, but if you have 2^256 ids, you have other problems.
- * (But actually, it's generally impossible to increment a counter this many times, energy wise
- * so it's not something you have to worry about.)
- */
-library Counter {
-    struct Counter {
-        uint256 current; // default: 0
-    }
-
-    function next(Counter storage index) internal returns (uint256) {
-        index.current += 1;
-        return index.current;
-    }
-}

contracts/drafts/Counters.sol

+pragma solidity ^0.5.2;
+
+import "../math/SafeMath.sol";
+
+/**
+ * @title Counters
+ * @author Matt Condon (@shrugs)
+ * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
+ * of elements in a mapping, issuing ERC721 ids, or counting request ids
+ *
+ * Include with `using Counters for Counters.Counter;`
+ * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the SafeMath
+ * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
+ * directly accessed.
+ */
+library Counters {
+    using SafeMath for uint256;
+
+    struct Counter {
+        // This variable should never be directly accessed by users of the library: interactions must be restricted to
+        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
+        // this feature: see https://github.com/ethereum/solidity/issues/4637
+        uint256 _value; // default: 0
+    }
+
+    function current(Counter storage counter) internal view returns (uint256) {
+        return counter._value;
+    }
+
+    function increment(Counter storage counter) internal {
+        counter._value += 1;
+    }
+
+    function decrement(Counter storage counter) internal {
+        counter._value = counter._value.sub(1);
+    }
+}

contracts/drafts/ERC1046/TokenMetadata.sol → contracts/drafts/ERC1046/ERC20Metadata.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../token/ERC20/IERC20.sol";
@@ -8,22 +8,20 @@ import "../../token/ERC20/IERC20.sol";
  * @dev See https://eips.ethereum.org/EIPS/eip-1046
  * @dev tokenURI must respond with a URI that implements https://eips.ethereum.org/EIPS/eip-1047
  */
-contract ERC20TokenMetadata is Initializable, IERC20 {
-    function tokenURI() external view returns (string memory);
-
-    uint256[50] private ______gap;
-}
-
-contract ERC20WithMetadata is Initializable, ERC20TokenMetadata {
+contract ERC20Metadata is Initializable {
     string private _tokenURI;
 
-    function initialize(string memory tokenURI) public {
-        _tokenURI = tokenURI;
+    function initialize(string memory tokenURI_) public {
+        _setTokenURI(tokenURI_);
     }
 
     function tokenURI() external view returns (string memory) {
         return _tokenURI;
     }
 
+    function _setTokenURI(string memory tokenURI_) internal {
+        _tokenURI = tokenURI_;
+    }
+
     uint256[50] private ______gap;
 }

contracts/drafts/ERC20Migrator.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../token/ERC20/IERC20.sol";
@@ -18,7 +18,7 @@ import "../math/Math.sol";
  * OpenZeppelin's ERC20Mintable, but the only functions that are needed are
  * `isMinter(address)` and `mint(address, amount)`. The migrator will check
  * that it is a minter for the token.
- * The balance from the legacy token will be transfered to the migrator, as it
+ * The balance from the legacy token will be transferred to the migrator, as it
  * is migrated, and remain there forever.
  * Although this contract can be used in many different scenarios, the main
  * motivation was to provide a way to migrate ERC20 tokens into an upgradeable
@@ -66,14 +66,14 @@ contract ERC20Migrator is Initializable {
     /**
      * @dev Begins the migration by setting which is the new token that will be
      * minted. This contract must be a minter for the new token.
-     * @param newToken the token that will be minted
+     * @param newToken_ the token that will be minted
      */
-    function beginMigration(ERC20Mintable newToken) public {
+    function beginMigration(ERC20Mintable newToken_) public {
         require(address(_newToken) == address(0));
-        require(address(newToken) != address(0));
-        require(newToken.isMinter(address(this)));
+        require(address(newToken_) != address(0));
+        require(newToken_.isMinter(address(this)));
 
-        _newToken = newToken;
+        _newToken = newToken_;
     }
 
     /**
@@ -83,6 +83,7 @@ contract ERC20Migrator is Initializable {
      * @param amount amount of tokens to be migrated
      */
     function migrate(address account, uint256 amount) public {
+        require(address(_newToken) != address(0));
         _legacyToken.safeTransferFrom(account, address(this), amount);
         _newToken.mint(account, amount);
     }

contracts/drafts/ERC20Snapshot.sol

+pragma solidity ^0.5.2;
+
+import "zos-lib/contracts/Initializable.sol";
+import "../math/SafeMath.sol";
+import "../utils/Arrays.sol";
+import "../drafts/Counters.sol";
+import "../token/ERC20/ERC20.sol";
+
+/**
+ * @title ERC20 token with snapshots.
+ * @dev Inspired by Jordi Baylina's MiniMeToken to record historical balances:
+ * https://github.com/Giveth/minime/blob/ea04d950eea153a04c51fa510b068b9dded390cb/contracts/MiniMeToken.sol
+ * When a snapshot is made, the balances and totalSupply at the time of the snapshot are recorded for later
+ * access.
+ *
+ * To make a snapshot, call the `snapshot` function, which will emit the `Snapshot` event and return a snapshot id.
+ * To get the total supply from a snapshot, call the function `totalSupplyAt` with the snapshot id.
+ * To get the balance of an account from a snapshot, call the `balanceOfAt` function with the snapshot id and the
+ * account address.
+ * @author Validity Labs AG <info@validitylabs.org>
+ */
+contract ERC20Snapshot is Initializable, ERC20 {
+    using SafeMath for uint256;
+    using Arrays for uint256[];
+    using Counters for Counters.Counter;
+
+    // Snapshotted values have arrays of ids and the value corresponding to that id. These could be an array of a
+    // Snapshot struct, but that would impede usage of functions that work on an array.
+    struct Snapshots {
+        uint256[] ids;
+        uint256[] values;
+    }
+
+    mapping (address => Snapshots) private _accountBalanceSnapshots;
+    Snapshots private _totalSupplySnaphots;
+
+    // Snapshot ids increase monotonically, with the first value being 1. An id of 0 is invalid.
+    Counters.Counter private _currentSnapshotId;
+
+    event Snapshot(uint256 id);
+
+    // Creates a new snapshot id. Balances are only stored in snapshots on demand: unless a snapshot was taken, a
+    // balance change will not be recorded. This means the extra added cost of storing snapshotted balances is only paid
+    // when required, but is also flexible enough that it allows for e.g. daily snapshots.
+    function snapshot() public returns (uint256) {
+        _currentSnapshotId.increment();
+
+        uint256 currentId = _currentSnapshotId.current();
+        emit Snapshot(currentId);
+        return currentId;
+    }
+
+    function balanceOfAt(address account, uint256 snapshotId) public view returns (uint256) {
+        (bool snapshotted, uint256 value) = _valueAt(snapshotId, _accountBalanceSnapshots[account]);
+
+        return snapshotted ? value : balanceOf(account);
+    }
+
+    function totalSupplyAt(uint256 snapshotId) public view returns(uint256) {
+        (bool snapshotted, uint256 value) = _valueAt(snapshotId, _totalSupplySnaphots);
+
+        return snapshotted ? value : totalSupply();
+    }
+
+    // _transfer, _mint and _burn are the only functions where the balances are modified, so it is there that the
+    // snapshots are updated. Note that the update happens _before_ the balance change, with the pre-modified value.
+    // The same is true for the total supply and _mint and _burn.
+    function _transfer(address from, address to, uint256 value) internal {
+        _updateAccountSnapshot(from);
+        _updateAccountSnapshot(to);
+
+        super._transfer(from, to, value);
+    }
+
+    function _mint(address account, uint256 value) internal {
+        _updateAccountSnapshot(account);
+        _updateTotalSupplySnapshot();
+
+        super._mint(account, value);
+    }
+
+    function _burn(address account, uint256 value) internal {
+        _updateAccountSnapshot(account);
+        _updateTotalSupplySnapshot();
+
+        super._burn(account, value);
+    }
+
+    // When a valid snapshot is queried, there are three possibilities:
+    //  a) The queried value was not modified after the snapshot was taken. Therefore, a snapshot entry was never
+    //  created for this id, and all stored snapshot ids are smaller than the requested one. The value that corresponds
+    //  to this id is the current one.
+    //  b) The queried value was modified after the snapshot was taken. Therefore, there will be an entry with the
+    //  requested id, and its value is the one to return.
+    //  c) More snapshots were created after the requested one, and the queried value was later modified. There will be
+    //  no entry for the requested id: the value that corresponds to it is that of the smallest snapshot id that is
+    //  larger than the requested one.
+    //
+    // In summary, we need to find an element in an array, returning the index of the smallest value that is larger if
+    // it is not found, unless said value doesn't exist (e.g. when all values are smaller). Arrays.findUpperBound does
+    // exactly this.
+    function _valueAt(uint256 snapshotId, Snapshots storage snapshots)
+        private view returns (bool, uint256)
+    {
+        require(snapshotId > 0);
+        require(snapshotId <= _currentSnapshotId.current());
+
+        uint256 index = snapshots.ids.findUpperBound(snapshotId);
+
+        if (index == snapshots.ids.length) {
+            return (false, 0);
+        } else {
+            return (true, snapshots.values[index]);
+        }
+    }
+
+    function _updateAccountSnapshot(address account) private {
+        _updateSnapshot(_accountBalanceSnapshots[account], balanceOf(account));
+    }
+
+    function _updateTotalSupplySnapshot() private {
+        _updateSnapshot(_totalSupplySnaphots, totalSupply());
+    }
+
+    function _updateSnapshot(Snapshots storage snapshots, uint256 currentValue) private {
+        uint256 currentId = _currentSnapshotId.current();
+        if (_lastSnapshotId(snapshots.ids) < currentId) {
+            snapshots.ids.push(currentId);
+            snapshots.values.push(currentValue);
+        }
+    }
+
+    function _lastSnapshotId(uint256[] storage ids) private view returns (uint256) {
+        if (ids.length == 0) {
+            return 0;
+        } else {
+            return ids[ids.length - 1];
+        }
+    }
+}

contracts/drafts/SignatureBouncer.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../access/roles/SignerRole.sol";
@@ -30,7 +30,7 @@ import "../cryptography/ECDSA.sol";
  * @notice A method that uses the `onlyValidSignatureAndData` modifier must make
  * the _signature parameter the "last" parameter. You cannot sign a message that
  * has its own signature in it so the last 128 bytes of msg.data (which
- * represents the length of the _signature data and the _signaature data itself)
+ * represents the length of the _signature data and the _signature data itself)
  * is ignored when validating. Also non fixed sized parameters make constructing
  * the data in the signature much more complex.
  * See https://ethereum.stackexchange.com/a/50616 for more details.
@@ -57,7 +57,7 @@ contract SignatureBouncer is Initializable, SignerRole {
     }
 
     /**
-     * @dev requires that a valid signature with a specifed method of a signer was provided
+     * @dev requires that a valid signature with a specified method of a signer was provided
      */
     modifier onlyValidSignatureAndMethod(bytes memory signature) {
         require(_isValidSignatureAndMethod(msg.sender, signature));
@@ -65,7 +65,7 @@ contract SignatureBouncer is Initializable, SignerRole {
     }
 
     /**
-     * @dev requires that a valid signature with a specifed method and params of a signer was provided
+     * @dev requires that a valid signature with a specified method and params of a signer was provided
      */
     modifier onlyValidSignatureAndData(bytes memory signature) {
         require(_isValidSignatureAndData(msg.sender, signature));
@@ -73,7 +73,7 @@ contract SignatureBouncer is Initializable, SignerRole {
     }
 
     /**
-     * @dev is the signature of `this + sender` from a signer?
+     * @dev is the signature of `this + account` from a signer?
      * @return bool
      */
     function _isValidSignature(address account, bytes memory signature) internal view returns (bool) {
@@ -81,7 +81,7 @@ contract SignatureBouncer is Initializable, SignerRole {
     }
 
     /**
-     * @dev is the signature of `this + sender + methodId` from a signer?
+     * @dev is the signature of `this + account + methodId` from a signer?
      * @return bool
      */
     function _isValidSignatureAndMethod(address account, bytes memory signature) internal view returns (bool) {
@@ -93,7 +93,7 @@ contract SignatureBouncer is Initializable, SignerRole {
     }
 
     /**
-        * @dev is the signature of `this + sender + methodId + params(s)` from a signer?
+     * @dev is the signature of `this + account + methodId + params(s)` from a signer?
      * @notice the signature parameter of the method being validated must be the "last" parameter
      * @return bool
      */

contracts/drafts/SignedSafeMath.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title SignedSafeMath

contracts/drafts/TokenVesting.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../token/ERC20/SafeERC20.sol";
@@ -14,8 +14,8 @@ import "../math/SafeMath.sol";
 contract TokenVesting is Initializable, Ownable {
     // The vesting schedule is time-based (i.e. using block timestamps as opposed to e.g. block numbers), and is
     // therefore sensitive to timestamp manipulation (which is something miners can do, to a certain degree). Therefore,
-    // it is recommended to avoid using short time durations (less than a minute). Typical vesting schemes, with a cliff
-    // period of a year and a duration of four years, are safe to use.
+    // it is recommended to avoid using short time durations (less than a minute). Typical vesting schemes, with a
+    // cliff period of a year and a duration of four years, are safe to use.
     // solhint-disable not-rely-on-time
 
     using SafeMath for uint256;

contracts/examples/SampleCrowdsale.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../crowdsale/validation/CappedCrowdsale.sol";

contracts/examples/SimpleToken.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../token/ERC20/ERC20.sol";

contracts/introspection/ERC165.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC165.sol";
@@ -10,7 +10,7 @@ import "./IERC165.sol";
  */
 contract ERC165 is Initializable, IERC165 {
     bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
-    /**
+    /*
      * 0x01ffc9a7 ===
      *     bytes4(keccak256('supportsInterface(bytes4)'))
      */

contracts/introspection/ERC165Checker.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title ERC165Checker
  * @dev Use `using ERC165Checker for address`; to include this library
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md
+ * https://eips.ethereum.org/EIPS/eip-165
  */
 library ERC165Checker {
     // As per the EIP-165 spec, no interface should ever match 0xffffffff
     bytes4 private constant _INTERFACE_ID_INVALID = 0xffffffff;
 
     bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;
-    /**
+    /*
      * 0x01ffc9a7 ===
      *     bytes4(keccak256('supportsInterface(bytes4)'))
      */

contracts/introspection/IERC165.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title IERC165
- * @dev https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md
+ * @dev https://eips.ethereum.org/EIPS/eip-165
  */
 interface IERC165 {
     /**

contracts/lifecycle/Pausable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../access/roles/PauserRole.sol";

contracts/math/Math.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title Math

contracts/math/SafeMath.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title SafeMath

contracts/mocks/Acknowledger.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 contract Acknowledger {
     event AcknowledgeFoo(uint256 a);

contracts/mocks/AddressImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../utils/Address.sol";
 

contracts/mocks/AllowanceCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/emission/AllowanceCrowdsale.sol";

contracts/mocks/ArraysImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../utils/Arrays.sol";
 

contracts/mocks/CappedCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/validation/CappedCrowdsale.sol";

contracts/mocks/CapperRoleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/roles/CapperRole.sol";
 

contracts/mocks/ConditionalEscrowMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../payment/escrow/ConditionalEscrow.sol";
 

contracts/mocks/CounterImpl.sol

-pragma solidity ^0.5.0;
-
-import "../drafts/Counter.sol";
-
-contract CounterImpl {
-    using Counter for Counter.Counter;
-
-    uint256 public theId;
-
-    // use whatever key you want to track your counters
-    mapping(string => Counter.Counter) private _counters;
-
-    function doThing(string memory key) public returns (uint256) {
-        theId = _counters[key].next();
-        return theId;
-    }
-}

contracts/mocks/CountersImpl.sol

+pragma solidity ^0.5.2;
+
+import "../drafts/Counters.sol";
+
+contract CountersImpl {
+    using Counters for Counters.Counter;
+
+    Counters.Counter private _counter;
+
+    function current() public view returns (uint256) {
+        return _counter.current();
+    }
+
+    function increment() public {
+        _counter.increment();
+    }
+
+    function decrement() public {
+        _counter.decrement();
+    }
+}

contracts/mocks/CrowdsaleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../crowdsale/Crowdsale.sol";
 

contracts/mocks/ECDSAMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../cryptography/ECDSA.sol";
 

contracts/mocks/ERC165/ERC165InterfacesSupported.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../../introspection/IERC165.sol";
 
 /**
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-214.md#specification
+ * https://eips.ethereum.org/EIPS/eip-214#specification
+ * From the specification:
  * > Any attempts to make state-changing operations inside an execution instance with STATIC set to true will instead
  * throw an exception.
  * > These operations include [...], LOG0, LOG1, LOG2, [...]
@@ -13,7 +14,7 @@ import "../../introspection/IERC165.sol";
  */
 contract SupportsInterfaceWithLookupMock is IERC165 {
     bytes4 public constant INTERFACE_ID_ERC165 = 0x01ffc9a7;
-    /**
+    /*
      * 0x01ffc9a7 ===
      *     bytes4(keccak256('supportsInterface(bytes4)'))
      */

contracts/mocks/ERC165/ERC165NotSupported.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 contract ERC165NotSupported {
     // solhint-disable-previous-line no-empty-blocks

contracts/mocks/ERC165CheckerMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../introspection/ERC165Checker.sol";
 

contracts/mocks/ERC165Mock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../introspection/ERC165.sol";
 

contracts/mocks/ERC20BurnableMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20Burnable.sol";
 

contracts/mocks/DetailedERC20Mock.sol → contracts/mocks/ERC20DetailedMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20.sol";
 import "../token/ERC20/ERC20Detailed.sol";

contracts/mocks/ERC20WithMetadataMock.sol → contracts/mocks/ERC20MetadataMock.sol

 pragma solidity ^0.5.0;
 
 import "../token/ERC20/ERC20.sol";
-import "../drafts/ERC1046/TokenMetadata.sol";
+import "../drafts/ERC1046/ERC20Metadata.sol";
 
-contract ERC20WithMetadataMock is ERC20, ERC20WithMetadata {
+contract ERC20MetadataMock is ERC20, ERC20Metadata {
     constructor (string memory tokenURI) public {
-        ERC20WithMetadata.initialize(tokenURI);
+        ERC20Metadata.initialize(tokenURI);
+    }
+
+    function setTokenURI(string memory tokenURI) public {
+        _setTokenURI(tokenURI);
     }
 }

contracts/mocks/ERC20MintableMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20Mintable.sol";
 import "./MinterRoleMock.sol";

contracts/mocks/ERC20Mock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20.sol";
 
@@ -19,4 +19,8 @@ contract ERC20Mock is ERC20 {
     function burnFrom(address account, uint256 amount) public {
         _burnFrom(account, amount);
     }
+
+    function approveInternal(address owner, address spender, uint256 value) public {
+        _approve(owner, spender, value);
+    }
 }

contracts/mocks/ERC20PausableMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20Pausable.sol";
 import "./PauserRoleMock.sol";

contracts/mocks/ERC20SnapshotMock.sol

+pragma solidity ^0.5.2;
+
+import "../drafts/ERC20Snapshot.sol";
+
+
+contract ERC20SnapshotMock is ERC20Snapshot {
+    constructor(address initialAccount, uint256 initialBalance) public {
+        _mint(initialAccount, initialBalance);
+    }
+
+    function mint(address account, uint256 amount) public {
+        _mint(account, amount);
+    }
+
+    function burn(address account, uint256 amount) public {
+        _burn(account, amount);
+    }
+}

contracts/mocks/ERC721FullMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC721/ERC721Full.sol";
 import "../token/ERC721/ERC721Mintable.sol";

contracts/mocks/ERC721MintableBurnableImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC721/ERC721Full.sol";
 import "../token/ERC721/ERC721Mintable.sol";

contracts/mocks/ERC721Mock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC721/ERC721.sol";
 

contracts/mocks/ERC721PausableMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC721/ERC721Pausable.sol";
 import "./PauserRoleMock.sol";

contracts/mocks/ERC721ReceiverMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC721/IERC721Receiver.sol";
 

contracts/mocks/EventEmitter.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 contract EventEmitter {
     event Argumentless();

contracts/mocks/Failer.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 contract Failer {
     uint256[] private array;

contracts/mocks/FinalizableCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/distribution/FinalizableCrowdsale.sol";

contracts/mocks/IncreasingPriceCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../crowdsale/price/IncreasingPriceCrowdsale.sol";
 import "../math/SafeMath.sol";

contracts/mocks/IndividuallyCappedCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/validation/IndividuallyCappedCrowdsale.sol";

contracts/mocks/MathMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../math/Math.sol";
 

contracts/mocks/MerkleProofWrapper.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import { MerkleProof } from "../cryptography/MerkleProof.sol";
 

contracts/mocks/MintedCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20Mintable.sol";
 import "../crowdsale/emission/MintedCrowdsale.sol";

contracts/mocks/MinterRoleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/roles/MinterRole.sol";
 

contracts/mocks/OwnableInterfaceId.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../ownership/Ownable.sol";
 
 /**
  * @title Ownable interface id calculator.
  * @dev See the EIP165 specification for more information:
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-165.md#specification
+ * https://eips.ethereum.org/EIPS/eip-165#specification
  */
 contract OwnableInterfaceId {
     function getInterfaceId() public pure returns (bytes4) {

contracts/mocks/OwnableMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../ownership/Ownable.sol";
 

contracts/mocks/PausableCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/ERC20.sol";
 import "../crowdsale/validation/PausableCrowdsale.sol";

contracts/mocks/PausableMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../lifecycle/Pausable.sol";
 import "./PauserRoleMock.sol";

contracts/mocks/PauserRoleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/roles/PauserRole.sol";
 

contracts/mocks/PostDeliveryCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/distribution/PostDeliveryCrowdsale.sol";

contracts/mocks/PullPaymentMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../payment/PullPayment.sol";
 

contracts/mocks/ReentrancyAttack.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 contract ReentrancyAttack {
     function callSender(bytes4 data) public {

contracts/mocks/ReentrancyMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../utils/ReentrancyGuard.sol";
 import "./ReentrancyAttack.sol";

contracts/mocks/RefundableCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/distribution/RefundableCrowdsale.sol";

contracts/mocks/RefundablePostDeliveryCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/distribution/RefundablePostDeliveryCrowdsale.sol";

contracts/mocks/RolesMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/Roles.sol";
 

contracts/mocks/SafeERC20Helper.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../token/ERC20/SafeERC20.sol";
 
-contract ERC20FailingMock {
+contract ERC20ReturnFalseMock {
     uint256 private _allowance;
 
+    // IERC20's functions are not pure, but these mock implementations are: to prevent Solidity from issuing warnings,
+    // we write to a dummy state variable.
+    uint256 private _dummy;
+
     function transfer(address, uint256) public returns (bool) {
+        _dummy = 0;
         return false;
     }
 
     function transferFrom(address, address, uint256) public returns (bool) {
+        _dummy = 0;
         return false;
     }
 
     function approve(address, uint256) public returns (bool) {
+        _dummy = 0;
         return false;
     }
 
     function allowance(address, address) public view returns (uint256) {
+        require(_dummy == 0);
         return 0;
     }
 }
 
-contract ERC20SucceedingMock {
-    uint256 private _allowance;
+contract ERC20ReturnTrueMock {
+    mapping (address => uint256) private _allowances;
+
+    // IERC20's functions are not pure, but these mock implementations are: to prevent Solidity from issuing warnings,
+    // we write to a dummy state variable.
+    uint256 private _dummy;
 
     function transfer(address, uint256) public returns (bool) {
+        _dummy = 0;
         return true;
     }
 
     function transferFrom(address, address, uint256) public returns (bool) {
+        _dummy = 0;
         return true;
     }
 
     function approve(address, uint256) public returns (bool) {
+        _dummy = 0;
         return true;
     }
 
     function setAllowance(uint256 allowance_) public {
-        _allowance = allowance_;
+        _allowances[msg.sender] = allowance_;
     }
 
-    function allowance(address, address) public view returns (uint256) {
-        return _allowance;
+    function allowance(address owner, address) public view returns (uint256) {
+        return _allowances[owner];
     }
 }
 
-contract SafeERC20Helper {
-    using SafeERC20 for IERC20;
+contract ERC20NoReturnMock {
+    mapping (address => uint256) private _allowances;
 
-    IERC20 private _failing;
-    IERC20 private _succeeding;
+    // IERC20's functions are not pure, but these mock implementations are: to prevent Solidity from issuing warnings,
+    // we write to a dummy state variable.
+    uint256 private _dummy;
 
-    constructor () public {
-        _failing = IERC20(address(new ERC20FailingMock()));
-        _succeeding = IERC20(address(new ERC20SucceedingMock()));
+    function transfer(address, uint256) public {
+        _dummy = 0;
     }
 
-    function doFailingTransfer() public {
-        _failing.safeTransfer(address(0), 0);
+    function transferFrom(address, address, uint256) public {
+        _dummy = 0;
     }
 
-    function doFailingTransferFrom() public {
-        _failing.safeTransferFrom(address(0), address(0), 0);
+    function approve(address, uint256) public {
+        _dummy = 0;
     }
 
-    function doFailingApprove() public {
-        _failing.safeApprove(address(0), 0);
+    function setAllowance(uint256 allowance_) public {
+        _allowances[msg.sender] = allowance_;
     }
 
-    function doFailingIncreaseAllowance() public {
-        _failing.safeIncreaseAllowance(address(0), 0);
+    function allowance(address owner, address) public view returns (uint256) {
+        return _allowances[owner];
     }
+}
+
+contract SafeERC20Wrapper {
+    using SafeERC20 for IERC20;
+
+    IERC20 private _token;
 
-    function doFailingDecreaseAllowance() public {
-        _failing.safeDecreaseAllowance(address(0), 0);
+    constructor (IERC20 token) public {
+        _token = token;
     }
 
-    function doSucceedingTransfer() public {
-        _succeeding.safeTransfer(address(0), 0);
+    function transfer() public {
+        _token.safeTransfer(address(0), 0);
     }
 
-    function doSucceedingTransferFrom() public {
-        _succeeding.safeTransferFrom(address(0), address(0), 0);
+    function transferFrom() public {
+        _token.safeTransferFrom(address(0), address(0), 0);
     }
 
-    function doSucceedingApprove(uint256 amount) public {
-        _succeeding.safeApprove(address(0), amount);
+    function approve(uint256 amount) public {
+        _token.safeApprove(address(0), amount);
     }
 
-    function doSucceedingIncreaseAllowance(uint256 amount) public {
-        _succeeding.safeIncreaseAllowance(address(0), amount);
+    function increaseAllowance(uint256 amount) public {
+        _token.safeIncreaseAllowance(address(0), amount);
     }
 
-    function doSucceedingDecreaseAllowance(uint256 amount) public {
-        _succeeding.safeDecreaseAllowance(address(0), amount);
+    function decreaseAllowance(uint256 amount) public {
+        _token.safeDecreaseAllowance(address(0), amount);
     }
 
     function setAllowance(uint256 allowance_) public {
-        ERC20SucceedingMock(address(_succeeding)).setAllowance(allowance_);
+        ERC20ReturnTrueMock(address(_token)).setAllowance(allowance_);
     }
 
     function allowance() public view returns (uint256) {
-        return _succeeding.allowance(address(0), address(0));
+        return _token.allowance(address(0), address(0));
     }
 }

contracts/mocks/SafeMathMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../math/SafeMath.sol";
 

contracts/mocks/SecondaryMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../ownership/Secondary.sol";
 

contracts/mocks/SignatureBouncerMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../drafts/SignatureBouncer.sol";
 import "./SignerRoleMock.sol";

contracts/mocks/SignedSafeMathMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../drafts/SignedSafeMath.sol";
 

contracts/mocks/SignerRoleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/roles/SignerRole.sol";
 

contracts/mocks/TimedCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/validation/TimedCrowdsale.sol";
@@ -10,4 +10,8 @@ contract TimedCrowdsaleImpl is TimedCrowdsale {
         Crowdsale.initialize(rate, wallet, token);
         TimedCrowdsale.initialize(openingTime, closingTime);
     }
+
+    function extendTime(uint256 closingTime) public {
+        _extendTime(closingTime);
+    }
 }

contracts/mocks/WhitelistAdminRoleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/roles/WhitelistAdminRole.sol";
 

contracts/mocks/WhitelistCrowdsaleImpl.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../token/ERC20/IERC20.sol";
 import "../crowdsale/validation/WhitelistCrowdsale.sol";

contracts/mocks/WhitelistedRoleMock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../access/roles/WhitelistedRole.sol";
 

contracts/ownership/Ownable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 
@@ -45,9 +45,10 @@ contract Ownable is Initializable {
 
     /**
      * @dev Allows the current owner to relinquish control of the contract.
-     * @notice Renouncing to ownership will leave the contract without an owner.
      * It will not be possible to call the functions with the `onlyOwner`
      * modifier anymore.
+     * @notice Renouncing ownership will leave the contract without an owner,
+     * thereby removing any functionality that is only available to the owner.
      */
     function renounceOwnership() public onlyOwner {
         emit OwnershipTransferred(_owner, address(0));

contracts/ownership/Secondary.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/payment/PaymentSplitter.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/payment/PullPayment.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

contracts/payment/escrow/ConditionalEscrow.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "./Escrow.sol";
 

contracts/payment/escrow/Escrow.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../../math/SafeMath.sol";
 import "../../ownership/Secondary.sol";

contracts/payment/escrow/RefundEscrow.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 
@@ -87,7 +87,7 @@ contract RefundEscrow is Initializable, ConditionalEscrow {
     }
 
     /**
-     * @dev Returns whether refundees can withdraw their deposits (be refunded). The overriden function receives a
+     * @dev Returns whether refundees can withdraw their deposits (be refunded). The overridden function receives a
      * 'payee' argument, but we ignore it here since the condition is global, not per-payee.
      */
     function withdrawalAllowed(address) public view returns (bool) {

contracts/token/ERC20/ERC20.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC20.sol";
@@ -8,7 +8,7 @@ import "../../math/SafeMath.sol";
  * @title Standard ERC20 token
  *
  * @dev Implementation of the basic standard token.
- * https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md
+ * https://eips.ethereum.org/EIPS/eip-20
  * Originally based on code by FirstBlood:
  * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
  *
@@ -35,7 +35,7 @@ contract ERC20 is Initializable, IERC20 {
     /**
      * @dev Gets the balance of the specified address.
      * @param owner The address to query the balance of.
-    * @return An uint256 representing the amount owned by the passed address.
+     * @return A uint256 representing the amount owned by the passed address.
      */
     function balanceOf(address owner) public view returns (uint256) {
         return _balances[owner];
@@ -52,7 +52,7 @@ contract ERC20 is Initializable, IERC20 {
     }
 
     /**
-    * @dev Transfer token for a specified address
+     * @dev Transfer token to a specified address
      * @param to The address to transfer to.
      * @param value The amount to be transferred.
      */
@@ -71,10 +71,7 @@ contract ERC20 is Initializable, IERC20 {
      * @param value The amount of tokens to be spent.
      */
     function approve(address spender, uint256 value) public returns (bool) {
-        require(spender != address(0));
-
-        _allowed[msg.sender][spender] = value;
-        emit Approval(msg.sender, spender, value);
+        _approve(msg.sender, spender, value);
         return true;
     }
 
@@ -87,15 +84,14 @@ contract ERC20 is Initializable, IERC20 {
      * @param value uint256 the amount of tokens to be transferred
      */
     function transferFrom(address from, address to, uint256 value) public returns (bool) {
-        _allowed[from][msg.sender] = _allowed[from][msg.sender].sub(value);
         _transfer(from, to, value);
-        emit Approval(from, msg.sender, _allowed[from][msg.sender]);
+        _approve(from, msg.sender, _allowed[from][msg.sender].sub(value));
         return true;
     }
 
     /**
      * @dev Increase the amount of tokens that an owner allowed to a spender.
-     * approve should be called when allowed_[_spender] == 0. To increment
+     * approve should be called when _allowed[msg.sender][spender] == 0. To increment
      * allowed value is better to use this function to avoid 2 calls (and wait until
      * the first transaction is mined)
      * From MonolithDAO Token.sol
@@ -104,16 +100,13 @@ contract ERC20 is Initializable, IERC20 {
      * @param addedValue The amount of tokens to increase the allowance by.
      */
     function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
-        require(spender != address(0));
-
-        _allowed[msg.sender][spender] = _allowed[msg.sender][spender].add(addedValue);
-        emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
+        _approve(msg.sender, spender, _allowed[msg.sender][spender].add(addedValue));
         return true;
     }
 
     /**
      * @dev Decrease the amount of tokens that an owner allowed to a spender.
-     * approve should be called when allowed_[_spender] == 0. To decrement
+     * approve should be called when _allowed[msg.sender][spender] == 0. To decrement
      * allowed value is better to use this function to avoid 2 calls (and wait until
      * the first transaction is mined)
      * From MonolithDAO Token.sol
@@ -122,10 +115,7 @@ contract ERC20 is Initializable, IERC20 {
      * @param subtractedValue The amount of tokens to decrease the allowance by.
      */
     function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
-        require(spender != address(0));
-
-        _allowed[msg.sender][spender] = _allowed[msg.sender][spender].sub(subtractedValue);
-        emit Approval(msg.sender, spender, _allowed[msg.sender][spender]);
+        _approve(msg.sender, spender, _allowed[msg.sender][spender].sub(subtractedValue));
         return true;
     }
 
@@ -173,6 +163,20 @@ contract ERC20 is Initializable, IERC20 {
     }
 
     /**
+     * @dev Approve an address to spend another addresses' tokens.
+     * @param owner The address that owns the tokens.
+     * @param spender The address that will spend the tokens.
+     * @param value The number of tokens that can be spent.
+     */
+    function _approve(address owner, address spender, uint256 value) internal {
+        require(spender != address(0));
+        require(owner != address(0));
+
+        _allowed[owner][spender] = value;
+        emit Approval(owner, spender, value);
+    }
+
+    /**
      * @dev Internal function that burns an amount of the token of a given
      * account, deducting from the sender's allowance for said account. Uses the
      * internal burn function.
@@ -181,9 +185,8 @@ contract ERC20 is Initializable, IERC20 {
      * @param value The amount that will be burnt.
      */
     function _burnFrom(address account, uint256 value) internal {
-        _allowed[account][msg.sender] = _allowed[account][msg.sender].sub(value);
         _burn(account, value);
-        emit Approval(account, msg.sender, _allowed[account][msg.sender]);
+        _approve(account, msg.sender, _allowed[account][msg.sender].sub(value));
     }
 
     uint256[50] private ______gap;

contracts/token/ERC20/ERC20Burnable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC20.sol";
@@ -18,8 +18,8 @@ contract ERC20Burnable is Initializable, ERC20 {
 
     /**
      * @dev Burns a specific amount of tokens from the target address and decrements allowance
-     * @param from address The address which you want to send tokens from
-     * @param value uint256 The amount of token to be burned
+     * @param from address The account whose tokens will be burned.
+     * @param value uint256 The amount of token to be burned.
      */
     function burnFrom(address from, uint256 value) public {
         _burnFrom(from, value);

contracts/token/ERC20/ERC20Capped.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC20Mintable.sol";

contracts/token/ERC20/ERC20Detailed.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC20.sol";

contracts/token/ERC20/ERC20Mintable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC20.sol";

contracts/token/ERC20/ERC20Pausable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC20.sol";
@@ -7,7 +7,7 @@ import "../../lifecycle/Pausable.sol";
 /**
  * @title Pausable token
  * @dev ERC20 modified with pausable transfers.
- **/
+ */
 contract ERC20Pausable is Initializable, ERC20, Pausable {
     function initialize(address sender) public initializer {
         Pausable.initialize(sender);

contracts/token/ERC20/IERC20.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title ERC20 interface
- * @dev see https://github.com/ethereum/EIPs/issues/20
+ * @dev see https://eips.ethereum.org/EIPS/eip-20
  */
 interface IERC20 {
     function transfer(address to, uint256 value) external returns (bool);

contracts/token/ERC20/SafeERC20.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "./IERC20.sol";
 import "../../math/SafeMath.sol";
+import "../../utils/Address.sol";
 
 /**
  * @title SafeERC20
- * @dev Wrappers around ERC20 operations that throw on failure.
+ * @dev Wrappers around ERC20 operations that throw on failure (when the token
+ * contract returns false). Tokens that return no value (and instead revert or
+ * throw on failure) are also supported, non-reverting calls are assumed to be
+ * successful.
  * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
  * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
  */
 library SafeERC20 {
     using SafeMath for uint256;
+    using Address for address;
 
     function safeTransfer(IERC20 token, address to, uint256 value) internal {
-        require(token.transfer(to, value));
+        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
     }
 
     function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
-        require(token.transferFrom(from, to, value));
+        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
     }
 
     function safeApprove(IERC20 token, address spender, uint256 value) internal {
         // safeApprove should only be called when setting an initial allowance,
         // or when resetting it to zero. To increase and decrease it, use
         // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
-        require((value == 0) || (token.allowance(msg.sender, spender) == 0));
-        require(token.approve(spender, value));
+        require((value == 0) || (token.allowance(address(this), spender) == 0));
+        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
     }
 
     function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
         uint256 newAllowance = token.allowance(address(this), spender).add(value);
-        require(token.approve(spender, newAllowance));
+        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
     }
 
     function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
         uint256 newAllowance = token.allowance(address(this), spender).sub(value);
-        require(token.approve(spender, newAllowance));
+        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
+    }
+
+    /**
+     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
+     * on the return value: the return value is optional (but if data is returned, it must equal true).
+     * @param token The token targeted by the call.
+     * @param data The call data (encoded using abi.encode or one of its variants).
+     */
+    function callOptionalReturn(IERC20 token, bytes memory data) private {
+        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
+        // we're implementing it ourselves.
+
+        // A Solidity high level call has three parts:
+        //  1. The target address is checked to verify it contains contract code
+        //  2. The call itself is made, and success asserted
+        //  3. The return value is decoded, which in turn checks the size of the returned data.
+
+        require(address(token).isContract());
+
+        // solhint-disable-next-line avoid-low-level-calls
+        (bool success, bytes memory returndata) = address(token).call(data);
+        require(success);
+
+        if (returndata.length > 0) { // Return data is optional
+            require(abi.decode(returndata, (bool)));
+        }
     }
 }

contracts/token/ERC20/TokenTimelock.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./SafeERC20.sol";

contracts/token/ERC721/ERC721.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC721.sol";
 import "./IERC721Receiver.sol";
 import "../../math/SafeMath.sol";
 import "../../utils/Address.sol";
+import "../../drafts/Counters.sol";
 import "../../introspection/ERC165.sol";
 
 /**
  * @title ERC721 Non-Fungible Token Standard basic implementation
- * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev see https://eips.ethereum.org/EIPS/eip-721
  */
 contract ERC721 is Initializable, ERC165, IERC721 {
     using SafeMath for uint256;
     using Address for address;
+    using Counters for Counters.Counter;
 
     // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
     // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
@@ -26,7 +28,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
     mapping (uint256 => address) private _tokenApprovals;
 
     // Mapping from owner to number of owned token
-    mapping (address => uint256) private _ownedTokensCount;
+    mapping (address => Counters.Counter) private _ownedTokensCount;
 
     // Mapping from owner to operator approvals
     mapping (address => mapping (address => bool)) private _operatorApprovals;
@@ -63,13 +65,13 @@ contract ERC721 is Initializable, ERC165, IERC721 {
      */
     function balanceOf(address owner) public view returns (uint256) {
         require(owner != address(0));
-        return _ownedTokensCount[owner];
+        return _ownedTokensCount[owner].current();
     }
 
     /**
      * @dev Gets the owner of the specified token ID
      * @param tokenId uint256 ID of the token to query the owner of
-     * @return owner address currently marked as the owner of the given token ID
+     * @return address currently marked as the owner of the given token ID
      */
     function ownerOf(uint256 tokenId) public view returns (address) {
         address owner = _tokenOwner[tokenId];
@@ -130,7 +132,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
     /**
      * @dev Transfers the ownership of a given token ID to another address
      * Usage of this method is discouraged, use `safeTransferFrom` whenever possible
-     * Requires the msg sender to be the owner, approved, or operator
+     * Requires the msg.sender to be the owner, approved, or operator
      * @param from current owner of the token
      * @param to address to receive the ownership of the given token ID
      * @param tokenId uint256 ID of the token to be transferred
@@ -147,8 +149,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
      * which is called upon a safe transfer, and return the magic value
      * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
      * the transfer is reverted.
-     *
-     * Requires the msg sender to be the owner, approved, or operator
+     * Requires the msg.sender to be the owner, approved, or operator
      * @param from current owner of the token
      * @param to address to receive the ownership of the given token ID
      * @param tokenId uint256 ID of the token to be transferred
@@ -163,7 +164,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
      * which is called upon a safe transfer, and return the magic value
      * `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`; otherwise,
      * the transfer is reverted.
-     * Requires the msg sender to be the owner, approved, or operator
+     * Requires the msg.sender to be the owner, approved, or operator
      * @param from current owner of the token
      * @param to address to receive the ownership of the given token ID
      * @param tokenId uint256 ID of the token to be transferred
@@ -177,7 +178,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
     /**
      * @dev Returns whether the specified token exists
      * @param tokenId uint256 ID of the token to query the existence of
-     * @return whether the token exists
+     * @return bool whether the token exists
      */
     function _exists(uint256 tokenId) internal view returns (bool) {
         address owner = _tokenOwner[tokenId];
@@ -207,7 +208,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
         require(!_exists(tokenId));
 
         _tokenOwner[tokenId] = to;
-        _ownedTokensCount[to] = _ownedTokensCount[to].add(1);
+        _ownedTokensCount[to].increment();
 
         emit Transfer(address(0), to, tokenId);
     }
@@ -224,7 +225,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
 
         _clearApproval(tokenId);
 
-        _ownedTokensCount[owner] = _ownedTokensCount[owner].sub(1);
+        _ownedTokensCount[owner].decrement();
         _tokenOwner[tokenId] = address(0);
 
         emit Transfer(owner, address(0), tokenId);
@@ -252,8 +253,8 @@ contract ERC721 is Initializable, ERC165, IERC721 {
 
         _clearApproval(tokenId);
 
-        _ownedTokensCount[from] = _ownedTokensCount[from].sub(1);
-        _ownedTokensCount[to] = _ownedTokensCount[to].add(1);
+        _ownedTokensCount[from].decrement();
+        _ownedTokensCount[to].increment();
 
         _tokenOwner[tokenId] = to;
 
@@ -267,7 +268,7 @@ contract ERC721 is Initializable, ERC165, IERC721 {
      * @param to target address that will receive the tokens
      * @param tokenId uint256 ID of the token to be transferred
      * @param _data bytes optional data to send along with the call
-     * @return whether the call correctly returned the expected magic value
+     * @return bool whether the call correctly returned the expected magic value
      */
     function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory _data)
         internal returns (bool)

contracts/token/ERC721/ERC721Burnable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721.sol";

contracts/token/ERC721/ERC721Enumerable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC721Enumerable.sol";
@@ -7,7 +7,7 @@ import "../../introspection/ERC165.sol";
 
 /**
  * @title ERC-721 Non-Fungible Token with optional enumeration extension logic
- * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev See https://eips.ethereum.org/EIPS/eip-721
  */
 contract ERC721Enumerable is Initializable, ERC165, ERC721, IERC721Enumerable {
     // Mapping from owner to list of owned token IDs
@@ -23,7 +23,7 @@ contract ERC721Enumerable is Initializable, ERC165, ERC721, IERC721Enumerable {
     mapping(uint256 => uint256) private _allTokensIndex;
 
     bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;
-    /**
+    /*
      * 0x780e9d63 ===
      *     bytes4(keccak256('totalSupply()')) ^
      *     bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) ^
@@ -35,8 +35,7 @@ contract ERC721Enumerable is Initializable, ERC165, ERC721, IERC721Enumerable {
      */
     function initialize() public initializer {
         require(ERC721._hasBeenInitialized());
-
-        // register the supported interface to conform to ERC721 via ERC165
+        // register the supported interface to conform to ERC721Enumerable via ERC165
         _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
     }
 
@@ -174,8 +173,8 @@ contract ERC721Enumerable is Initializable, ERC165, ERC721, IERC721Enumerable {
         // This also deletes the contents at the last position of the array
         _ownedTokens[from].length--;
 
-        // Note that _ownedTokensIndex[tokenId] hasn't been cleared: it still points to the old slot (now occcupied by
-        // lasTokenId, or just over the end of the array if the token was the last one).
+        // Note that _ownedTokensIndex[tokenId] hasn't been cleared: it still points to the old slot (now occupied by
+        // lastTokenId, or just over the end of the array if the token was the last one).
     }
 
     /**

contracts/token/ERC721/ERC721Full.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721.sol";
@@ -9,7 +9,7 @@ import "./ERC721Metadata.sol";
  * @title Full ERC721 Token
  * This implementation includes all the required and some optional functionality of the ERC721 standard
  * Moreover, it includes approve all functionality using operator terminology
- * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev see https://eips.ethereum.org/EIPS/eip-721
  */
 contract ERC721Full is Initializable, ERC721, ERC721Enumerable, ERC721Metadata {
     uint256[50] private ______gap;

contracts/token/ERC721/ERC721Holder.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC721Receiver.sol";

contracts/token/ERC721/ERC721Metadata.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721.sol";
@@ -16,7 +16,7 @@ contract ERC721Metadata is Initializable, ERC165, ERC721, IERC721Metadata {
     mapping(uint256 => string) private _tokenURIs;
 
     bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;
-    /**
+    /*
      * 0x5b5e139f ===
      *     bytes4(keccak256('name()')) ^
      *     bytes4(keccak256('symbol()')) ^

contracts/token/ERC721/ERC721MetadataMintable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721Metadata.sol";

contracts/token/ERC721/ERC721Mintable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721.sol";

contracts/token/ERC721/ERC721Pausable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./ERC721.sol";
@@ -7,7 +7,7 @@ import "../../lifecycle/Pausable.sol";
 /**
  * @title ERC721 Non-Fungible Pausable token
  * @dev ERC721 modified with pausable transfers.
- **/
+ */
 contract ERC721Pausable is Initializable, ERC721, Pausable {
     function initialize(address sender) public initializer {
         require(ERC721._hasBeenInitialized());

contracts/token/ERC721/IERC721.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "../../introspection/IERC165.sol";
 
 /**
  * @title ERC721 Non-Fungible Token Standard basic interface
- * @dev see https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev see https://eips.ethereum.org/EIPS/eip-721
  */
 contract IERC721 is Initializable, IERC165 {
     event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

contracts/token/ERC721/IERC721Enumerable.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC721.sol";
 
 /**
  * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
- * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev See https://eips.ethereum.org/EIPS/eip-721
  */
 contract IERC721Enumerable is Initializable, IERC721 {
     function totalSupply() public view returns (uint256);

contracts/token/ERC721/IERC721Full.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC721.sol";
@@ -7,7 +7,7 @@ import "./IERC721Metadata.sol";
 
 /**
  * @title ERC-721 Non-Fungible Token Standard, full implementation interface
- * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev See https://eips.ethereum.org/EIPS/eip-721
  */
 contract IERC721Full is Initializable, IERC721, IERC721Enumerable, IERC721Metadata {
     // solhint-disable-previous-line no-empty-blocks

contracts/token/ERC721/IERC721Metadata.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 import "./IERC721.sol";
 
 /**
  * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
- * @dev See https://github.com/ethereum/EIPs/blob/master/EIPS/eip-721.md
+ * @dev See https://eips.ethereum.org/EIPS/eip-721
  */
 contract IERC721Metadata is Initializable, IERC721 {
     function name() external view returns (string memory);

contracts/token/ERC721/IERC721Receiver.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * @title ERC721 token receiver interface
@@ -18,7 +18,7 @@ contract IERC721Receiver {
      * @param from The address which previously owned the token
      * @param tokenId The NFT identifier which is being transferred
      * @param data Additional data with no specified format
-     * @return `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
+     * @return bytes4 `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
      */
     function onERC721Received(address operator, address from, uint256 tokenId, bytes memory data)
     public returns (bytes4);

contracts/utils/Address.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 /**
  * Utility library of inline functions on addresses

contracts/utils/Arrays.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "../math/Math.sol";
 
@@ -9,13 +9,13 @@ import "../math/Math.sol";
  */
 library Arrays {
     /**
-     * @dev Upper bound search function which is kind of binary search algoritm. It searches sorted
-     * array to find index of the element value. If element is found then returns it's index otherwise
-     * it returns index of first element which is grater than searched value. If searched element is
+     * @dev Upper bound search function which is kind of binary search algorithm. It searches sorted
+     * array to find index of the element value. If element is found then returns its index otherwise
+     * it returns index of first element which is greater than searched value. If searched element is
      * bigger than any array element function then returns first index after last element (i.e. all
      * values inside the array are smaller than the target). Complexity O(log n).
      * @param array The array sorted in ascending order.
-     * @param element The element's value to be find.
+     * @param element The element's value to be found.
      * @return The calculated index value. Returns 0 for empty array.
      */
     function findUpperBound(uint256[] storage array, uint256 element) internal view returns (uint256) {

contracts/utils/ReentrancyGuard.sol

-pragma solidity ^0.5.0;
+pragma solidity ^0.5.2;
 
 import "zos-lib/contracts/Initializable.sol";
 

package.json

 {
   "name": "openzeppelin-eth",
-  "version": "2.1.3",
+  "version": "2.2.0",
   "description": "Secure Smart Contract library for Solidity",
   "files": [
     "build",
@@ -58,7 +58,7 @@
     "openzeppelin-test-helpers": "^0.1.1",
     "pify": "^4.0.1",
     "solhint": "^1.5.0",
-    "solidity-coverage": "^0.5.4",
+    "solidity-coverage": "https://github.com:rotcivegaf/solidity-coverage.git#5875f5b7bc74d447f3312c9c0e9fc7814b482477",
     "truffle": "^5.0.0",
     "zos": "^2.0.0",
     "zos-lib": "^2.1.0"

test/crowdsale/AllowanceCrowdsale.test.js

@@ -54,7 +54,7 @@ contract('AllowanceCrowdsale', function ([_, investor, wallet, purchaser, tokenW
   });
 
   describe('check remaining allowance', function () {
-    it('should report correct allowace left', async function () {
+    it('should report correct allowance left', async function () {
       const remainingAllowance = tokenAllowance.sub(expectedTokenAmount);
       await this.crowdsale.buyTokens(investor, { value: value, from: purchaser });
       (await this.crowdsale.remainingTokens()).should.be.bignumber.equal(remainingAllowance);
@@ -72,7 +72,7 @@ contract('AllowanceCrowdsale', function ([_, investor, wallet, purchaser, tokenW
     });
   });
 
-  describe('when token wallet is different from token address', function () {
+  describe('when token wallet is the zero address', function () {
     it('creation reverts', async function () {
       this.token = await SimpleToken.new({ from: tokenWallet });
       await shouldFail.reverting(AllowanceCrowdsaleImpl.new(rate, wallet, this.token.address, ZERO_ADDRESS));

test/crowdsale/IncreasingPriceCrowdsale.test.js

@@ -31,7 +31,7 @@ contract('IncreasingPriceCrowdsale', function ([_, investor, wallet, purchaser])
       ));
     });
 
-    it('reverts with a final equal to the initial rate', async function () {
+    it('reverts with a final rate equal to the initial rate', async function () {
       await shouldFail.reverting(IncreasingPriceCrowdsaleImpl.new(
         this.startTime, this.closingTime, wallet, this.token.address, initialRate, initialRate
       ));

test/crowdsale/TimedCrowdsale.test.js

-const { BN, ether, shouldFail, time } = require('openzeppelin-test-helpers');
+const { BN, ether, expectEvent, shouldFail, time } = require('openzeppelin-test-helpers');
 
 const TimedCrowdsaleImpl = artifacts.require('TimedCrowdsaleImpl');
 const SimpleToken = artifacts.require('SimpleTokenMock');
@@ -73,5 +73,62 @@ contract('TimedCrowdsale', function ([_, investor, wallet, purchaser]) {
         await shouldFail.reverting(this.crowdsale.buyTokens(investor, { value: value, from: purchaser }));
       });
     });
+
+    describe('extending closing time', function () {
+      it('should not reduce duration', async function () {
+        // Same date
+        await shouldFail.reverting(this.crowdsale.extendTime(this.closingTime));
+
+        // Prescending date
+        const newClosingTime = this.closingTime.sub(time.duration.seconds(1));
+        await shouldFail.reverting(this.crowdsale.extendTime(newClosingTime));
+      });
+
+      context('before crowdsale start', function () {
+        beforeEach(async function () {
+          (await this.crowdsale.isOpen()).should.equal(false);
+          await shouldFail.reverting(this.crowdsale.send(value));
+        });
+
+        it('it extends end time', async function () {
+          const newClosingTime = this.closingTime.add(time.duration.days(1));
+          const { logs } = await this.crowdsale.extendTime(newClosingTime);
+          expectEvent.inLogs(logs, 'TimedCrowdsaleExtended', {
+            prevClosingTime: this.closingTime,
+            newClosingTime: newClosingTime,
+          });
+          (await this.crowdsale.closingTime()).should.be.bignumber.equal(newClosingTime);
+        });
+      });
+
+      context('after crowdsale start', function () {
+        beforeEach(async function () {
+          await time.increaseTo(this.openingTime);
+          (await this.crowdsale.isOpen()).should.equal(true);
+          await this.crowdsale.send(value);
+        });
+
+        it('it extends end time', async function () {
+          const newClosingTime = this.closingTime.add(time.duration.days(1));
+          const { logs } = await this.crowdsale.extendTime(newClosingTime);
+          expectEvent.inLogs(logs, 'TimedCrowdsaleExtended', {
+            prevClosingTime: this.closingTime,
+            newClosingTime: newClosingTime,
+          });
+          (await this.crowdsale.closingTime()).should.be.bignumber.equal(newClosingTime);
+        });
+      });
+
+      context('after crowdsale end', function () {
+        beforeEach(async function () {
+          await time.increaseTo(this.afterClosingTime);
+        });
+
+        it('it reverts', async function () {
+          const newClosingTime = await time.latest();
+          await shouldFail.reverting(this.crowdsale.extendTime(newClosingTime));
+        });
+      });
+    });
   });
 });

test/cryptography/ECDSA.test.js

-const { shouldFail } = require('openzeppelin-test-helpers');
-const { signMessage, toEthSignedMessageHash } = require('../helpers/sign');
+const { constants, shouldFail } = require('openzeppelin-test-helpers');
+const { ZERO_ADDRESS } = constants;
+const { toEthSignedMessageHash, fixSignature } = require('../helpers/sign');
 
 const ECDSAMock = artifacts.require('ECDSAMock');
 
@@ -19,10 +20,10 @@ contract('ECDSA', function ([_, anyone]) {
       const signatureWithoutVersion = '0x5d99b6f7f6d1f73d1a26497f2b1c89b24c0993913f86e9a2d02cd69887d9c94f3c880358579d811b21dd1b7fd9bb01c1d81d10e69f0384e675c32b39643be892';
 
       context('with 00 as version value', function () {
-        it('works', async function () {
+        it('returns 0', async function () {
           const version = '00';
           const signature = signatureWithoutVersion + version;
-          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(signer);
+          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(ZERO_ADDRESS);
         });
       });
 
@@ -40,8 +41,7 @@ contract('ECDSA', function ([_, anyone]) {
           // The only valid values are 0, 1, 27 and 28.
           const version = '02';
           const signature = signatureWithoutVersion + version;
-          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(
-            '0x0000000000000000000000000000000000000000');
+          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(ZERO_ADDRESS);
         });
       });
     });
@@ -52,14 +52,14 @@ contract('ECDSA', function ([_, anyone]) {
       const signatureWithoutVersion = '0x331fe75a821c982f9127538858900d87d3ec1f9f737338ad67cad133fa48feff48e6fa0c18abc62e42820f05943e47af3e9fbe306ce74d64094bdf1691ee53e0';
 
       context('with 01 as version value', function () {
-        it('works', async function () {
+        it('returns 0', async function () {
           const version = '01';
           const signature = signatureWithoutVersion + version;
-          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(signer);
+          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(ZERO_ADDRESS);
         });
       });
 
-      context('with 28 signature', function () {
+      context('with 28 as version value', function () {
         it('works', async function () {
           const version = '1c'; // 28 = 1c.
           const signature = signatureWithoutVersion + version;
@@ -73,17 +73,26 @@ contract('ECDSA', function ([_, anyone]) {
           // The only valid values are 0, 1, 27 and 28.
           const version = '02';
           const signature = signatureWithoutVersion + version;
-          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(
-            '0x0000000000000000000000000000000000000000');
+          (await this.ecdsa.recover(TEST_MESSAGE, signature)).should.equal(ZERO_ADDRESS);
+        });
       });
     });
+
+    context('with high-s value signature', function () {
+      it('returns 0', async function () {
+        const message = '0xb94d27b9934d3e08a52e52d7da7dabfac484efe37a5380ee9088f7ace2efcde9';
+        // eslint-disable-next-line max-len
+        const highSSignature = '0xe742ff452d41413616a5bf43fe15dd88294e983d3d36206c2712f39083d638bde0a0fc89be718fbc1033e1d30d78be1c68081562ed2e97af876f286f3453231d1b';
+
+        (await this.ecdsa.recover(message, highSSignature)).should.equal(ZERO_ADDRESS);
+      });
     });
 
     context('using web3.eth.sign', function () {
       context('with correct signature', function () {
         it('returns signer address', async function () {
           // Create the signature
-          const signature = await signMessage(anyone, TEST_MESSAGE);
+          const signature = fixSignature(await web3.eth.sign(TEST_MESSAGE, anyone));
 
           // Recover the signer address from the generated message and signature.
           (await this.ecdsa.recover(
@@ -96,25 +105,25 @@ contract('ECDSA', function ([_, anyone]) {
       context('with wrong signature', function () {
         it('does not return signer address', async function () {
           // Create the signature
-          const signature = await signMessage(anyone, TEST_MESSAGE);
+          const signature = await web3.eth.sign(TEST_MESSAGE, anyone);
 
           // Recover the signer address from the generated message and wrong signature.
           (await this.ecdsa.recover(WRONG_MESSAGE, signature)).should.not.equal(anyone);
         });
       });
     });
-  });
 
     context('with small hash', function () {
       // @TODO - remove `skip` once we upgrade to solc^0.5
       it.skip('reverts', async function () {
         // Create the signature
-      const signature = await signMessage(anyone, TEST_MESSAGE);
+        const signature = await web3.eth.sign(TEST_MESSAGE, anyone);
         await shouldFail.reverting(
           this.ecdsa.recover(TEST_MESSAGE.substring(2), signature)
         );
       });
     });
+  });
 
   context('toEthSignedMessage', function () {
     it('should prefix hashes correctly', async function () {

test/drafts/Counter.test.js

-const { BN } = require('openzeppelin-test-helpers');
-
-const CounterImpl = artifacts.require('CounterImpl');
-
-const EXPECTED = [new BN(1), new BN(2), new BN(3), new BN(4)];
-const KEY1 = web3.utils.sha3('key1');
-const KEY2 = web3.utils.sha3('key2');
-
-contract('Counter', function ([_, owner]) {
-  beforeEach(async function () {
-    this.mock = await CounterImpl.new({ from: owner });
-  });
-
-  context('custom key', async function () {
-    it('should return expected values', async function () {
-      for (const expectedId of EXPECTED) {
-        await this.mock.doThing(KEY1, { from: owner });
-        const actualId = await this.mock.theId();
-        actualId.should.be.bignumber.equal(expectedId);
-      }
-    });
-  });
-
-  context('parallel keys', async function () {
-    it('should return expected values for each counter', async function () {
-      for (const expectedId of EXPECTED) {
-        await this.mock.doThing(KEY1, { from: owner });
-        let actualId = await this.mock.theId();
-        actualId.should.be.bignumber.equal(expectedId);
-
-        await this.mock.doThing(KEY2, { from: owner });
-        actualId = await this.mock.theId();
-        actualId.should.be.bignumber.equal(expectedId);
-      }
-    });
-  });
-});

test/drafts/Counters.test.js

+const { shouldFail } = require('openzeppelin-test-helpers');
+
+const CountersImpl = artifacts.require('CountersImpl');
+
+contract('Counters', function () {
+  beforeEach(async function () {
+    this.counter = await CountersImpl.new();
+  });
+
+  it('starts at zero', async function () {
+    (await this.counter.current()).should.be.bignumber.equal('0');
+  });
+
+  describe('increment', function () {
+    it('increments the current value by one', async function () {
+      await this.counter.increment();
+      (await this.counter.current()).should.be.bignumber.equal('1');
+    });
+
+    it('can be called multiple times', async function () {
+      await this.counter.increment();
+      await this.counter.increment();
+      await this.counter.increment();
+
+      (await this.counter.current()).should.be.bignumber.equal('3');
+    });
+  });
+
+  describe('decrement', function () {
+    beforeEach(async function () {
+      await this.counter.increment();
+      (await this.counter.current()).should.be.bignumber.equal('1');
+    });
+
+    it('decrements the current value by one', async function () {
+      await this.counter.decrement();
+      (await this.counter.current()).should.be.bignumber.equal('0');
+    });
+
+    it('reverts if the current value is 0', async function () {
+      await this.counter.decrement();
+      await shouldFail.reverting(this.counter.decrement());
+    });
+
+    it('can be called multiple times', async function () {
+      await this.counter.increment();
+      await this.counter.increment();
+
+      (await this.counter.current()).should.be.bignumber.equal('3');
+
+      await this.counter.decrement();
+      await this.counter.decrement();
+      await this.counter.decrement();
+
+      (await this.counter.current()).should.be.bignumber.equal('0');
+    });
+  });
+});

test/drafts/ERC1046/TokenMetadata.test.js → test/drafts/ERC1046/ERC20Metadata.test.js

 require('openzeppelin-test-helpers');
 
-const ERC20WithMetadataMock = artifacts.require('ERC20WithMetadataMock');
+const ERC20MetadataMock = artifacts.require('ERC20MetadataMock');
 
 const metadataURI = 'https://example.com';
 
-describe('ERC20WithMetadata', function () {
+describe('ERC20Metadata', function () {
   beforeEach(async function () {
-    this.token = await ERC20WithMetadataMock.new(metadataURI);
+    this.token = await ERC20MetadataMock.new(metadataURI);
   });
 
   it('responds with the metadata', async function () {
     (await this.token.tokenURI()).should.equal(metadataURI);
   });
+
+  describe('setTokenURI', function () {
+    it('changes the original URI', async function () {
+      const newMetadataURI = 'https://betterexample.com';
+      await this.token.setTokenURI(newMetadataURI);
+      (await this.token.tokenURI()).should.equal(newMetadataURI);
+    });
+  });
 });

test/drafts/ERC20Migrator.test.js

@@ -44,6 +44,40 @@ contract('ERC20Migrator', function ([_, owner, recipient, anotherAccount]) {
       });
     });
 
+    context('before starting the migration', function () {
+      it('returns the zero address for the new token', async function () {
+        (await this.migrator.newToken()).should.be.equal(ZERO_ADDRESS);
+      });
+
+      describe('migrateAll', function () {
+        const amount = totalSupply;
+
+        describe('when the approved balance is equal to the owned balance', function () {
+          beforeEach('approving the whole balance to the new contract', async function () {
+            await this.legacyToken.approve(this.migrator.address, amount, { from: owner });
+          });
+
+          it('reverts', async function () {
+            await shouldFail.reverting(this.migrator.migrateAll(owner));
+          });
+        });
+      });
+
+      describe('migrate', function () {
+        const amount = new BN(50);
+
+        describe('when the amount is equal to the approved value', function () {
+          beforeEach('approving tokens to the new contract', async function () {
+            await this.legacyToken.approve(this.migrator.address, amount, { from: owner });
+          });
+
+          it('reverts', async function () {
+            await shouldFail.reverting(this.migrator.migrate(owner, amount));
+          });
+        });
+      });
+    });
+
     describe('once migration began', function () {
       beforeEach('beginning migration', async function () {
         await this.newToken.addMinter(this.migrator.address);

test/drafts/ERC20Snapshot.test.js

+const { BN, expectEvent, shouldFail } = require('openzeppelin-test-helpers');
+const ERC20SnapshotMock = artifacts.require('ERC20SnapshotMock');
+
+contract('ERC20Snapshot', function ([_, initialHolder, recipient, anyone]) {
+  const initialSupply = new BN(100);
+
+  beforeEach(async function () {
+    this.token = await ERC20SnapshotMock.new(initialHolder, initialSupply);
+  });
+
+  describe('snapshot', function () {
+    it('emits a snapshot event', async function () {
+      const { logs } = await this.token.snapshot();
+      expectEvent.inLogs(logs, 'Snapshot');
+    });
+
+    it('creates increasing snapshots ids, starting from 1', async function () {
+      for (const id of ['1', '2', '3', '4', '5']) {
+        const { logs } = await this.token.snapshot();
+        expectEvent.inLogs(logs, 'Snapshot', { id });
+      }
+    });
+  });
+
+  describe('totalSupplyAt', function () {
+    it('reverts with a snapshot id of 0', async function () {
+      await shouldFail.reverting(this.token.totalSupplyAt(0));
+    });
+
+    it('reverts with a not-yet-created snapshot id', async function () {
+      await shouldFail.reverting(this.token.totalSupplyAt(1));
+    });
+
+    context('with initial snapshot', function () {
+      beforeEach(async function () {
+        this.initialSnapshotId = new BN('1');
+
+        const { logs } = await this.token.snapshot();
+        expectEvent.inLogs(logs, 'Snapshot', { id: this.initialSnapshotId });
+      });
+
+      context('with no supply changes after the snapshot', function () {
+        it('returns the current total supply', async function () {
+          (await this.token.totalSupplyAt(this.initialSnapshotId)).should.be.bignumber.equal(initialSupply);
+        });
+      });
+
+      context('with supply changes after the snapshot', function () {
+        beforeEach(async function () {
+          await this.token.mint(anyone, new BN('50'));
+          await this.token.burn(initialHolder, new BN('20'));
+        });
+
+        it('returns the total supply before the changes', async function () {
+          (await this.token.totalSupplyAt(this.initialSnapshotId)).should.be.bignumber.equal(initialSupply);
+        });
+
+        context('with a second snapshot after supply changes', function () {
+          beforeEach(async function () {
+            this.secondSnapshotId = new BN('2');
+
+            const { logs } = await this.token.snapshot();
+            expectEvent.inLogs(logs, 'Snapshot', { id: this.secondSnapshotId });
+          });
+
+          it('snapshots return the supply before and after the changes', async function () {
+            (await this.token.totalSupplyAt(this.initialSnapshotId)).should.be.bignumber.equal(initialSupply);
+
+            (await this.token.totalSupplyAt(this.secondSnapshotId)).should.be.bignumber.equal(
+              await this.token.totalSupply()
+            );
+          });
+        });
+
+        context('with multiple snapshots after supply changes', function () {
+          beforeEach(async function () {
+            this.secondSnapshotIds = ['2', '3', '4'];
+
+            for (const id of this.secondSnapshotIds) {
+              const { logs } = await this.token.snapshot();
+              expectEvent.inLogs(logs, 'Snapshot', { id });
+            }
+          });
+
+          it('all posterior snapshots return the supply after the changes', async function () {
+            (await this.token.totalSupplyAt(this.initialSnapshotId)).should.be.bignumber.equal(initialSupply);
+
+            const currentSupply = await this.token.totalSupply();
+
+            for (const id of this.secondSnapshotIds) {
+              (await this.token.totalSupplyAt(id)).should.be.bignumber.equal(currentSupply);
+            }
+          });
+        });
+      });
+    });
+  });
+
+  describe('balanceOfAt', function () {
+    it('reverts with a snapshot id of 0', async function () {
+      await shouldFail.reverting(this.token.balanceOfAt(anyone, 0));
+    });
+
+    it('reverts with a not-yet-created snapshot id', async function () {
+      await shouldFail.reverting(this.token.balanceOfAt(anyone, 1));
+    });
+
+    context('with initial snapshot', function () {
+      beforeEach(async function () {
+        this.initialSnapshotId = new BN('1');
+
+        const { logs } = await this.token.snapshot();
+        expectEvent.inLogs(logs, 'Snapshot', { id: this.initialSnapshotId });
+      });
+
+      context('with no balance changes after the snapshot', function () {
+        it('returns the current balance for all accounts', async function () {
+          (await this.token.balanceOfAt(initialHolder, this.initialSnapshotId))
+            .should.be.bignumber.equal(initialSupply);
+          (await this.token.balanceOfAt(recipient, this.initialSnapshotId)).should.be.bignumber.equal('0');
+          (await this.token.balanceOfAt(anyone, this.initialSnapshotId)).should.be.bignumber.equal('0');
+        });
+      });
+
+      context('with balance changes after the snapshot', function () {
+        beforeEach(async function () {
+          await this.token.transfer(recipient, new BN('10'), { from: initialHolder });
+          await this.token.mint(recipient, new BN('50'));
+          await this.token.burn(initialHolder, new BN('20'));
+        });
+
+        it('returns the balances before the changes', async function () {
+          (await this.token.balanceOfAt(initialHolder, this.initialSnapshotId))
+            .should.be.bignumber.equal(initialSupply);
+          (await this.token.balanceOfAt(recipient, this.initialSnapshotId)).should.be.bignumber.equal('0');
+          (await this.token.balanceOfAt(anyone, this.initialSnapshotId)).should.be.bignumber.equal('0');
+        });
+
+        context('with a second snapshot after supply changes', function () {
+          beforeEach(async function () {
+            this.secondSnapshotId = new BN('2');
+
+            const { logs } = await this.token.snapshot();
+            expectEvent.inLogs(logs, 'Snapshot', { id: this.secondSnapshotId });
+          });
+
+          it('snapshots return the balances before and after the changes', async function () {
+            (await this.token.balanceOfAt(initialHolder, this.initialSnapshotId))
+              .should.be.bignumber.equal(initialSupply);
+            (await this.token.balanceOfAt(recipient, this.initialSnapshotId)).should.be.bignumber.equal('0');
+            (await this.token.balanceOfAt(anyone, this.initialSnapshotId)).should.be.bignumber.equal('0');
+
+            (await this.token.balanceOfAt(initialHolder, this.secondSnapshotId)).should.be.bignumber.equal(
+              await this.token.balanceOf(initialHolder)
+            );
+            (await this.token.balanceOfAt(recipient, this.secondSnapshotId)).should.be.bignumber.equal(
+              await this.token.balanceOf(recipient)
+            );
+            (await this.token.balanceOfAt(anyone, this.secondSnapshotId)).should.be.bignumber.equal(
+              await this.token.balanceOf(anyone)
+            );
+          });
+        });
+
+        context('with multiple snapshots after supply changes', function () {
+          beforeEach(async function () {
+            this.secondSnapshotIds = ['2', '3', '4'];
+
+            for (const id of this.secondSnapshotIds) {
+              const { logs } = await this.token.snapshot();
+              expectEvent.inLogs(logs, 'Snapshot', { id });
+            }
+          });
+
+          it('all posterior snapshots return the supply after the changes', async function () {
+            (await this.token.balanceOfAt(initialHolder, this.initialSnapshotId))
+              .should.be.bignumber.equal(initialSupply);
+            (await this.token.balanceOfAt(recipient, this.initialSnapshotId)).should.be.bignumber.equal('0');
+            (await this.token.balanceOfAt(anyone, this.initialSnapshotId)).should.be.bignumber.equal('0');
+
+            for (const id of this.secondSnapshotIds) {
+              (await this.token.balanceOfAt(initialHolder, id)).should.be.bignumber.equal(
+                await this.token.balanceOf(initialHolder)
+              );
+              (await this.token.balanceOfAt(recipient, id)).should.be.bignumber.equal(
+                await this.token.balanceOf(recipient)
+              );
+              (await this.token.balanceOfAt(anyone, id)).should.be.bignumber.equal(
+                await this.token.balanceOf(anyone)
+              );
+            }
+          });
+        });
+      });
+    });
+  });
+});

test/drafts/SignedSafeMath.test.js

@@ -8,34 +8,43 @@ contract('SignedSafeMath', function () {
     this.safeMath = await SignedSafeMathMock.new();
   });
 
+  async function testCommutative (fn, lhs, rhs, expected) {
+    (await fn(lhs, rhs)).should.be.bignumber.equal(expected);
+    (await fn(rhs, lhs)).should.be.bignumber.equal(expected);
+  }
+
+  async function testFailsCommutative (fn, lhs, rhs) {
+    await shouldFail.reverting(fn(lhs, rhs));
+    await shouldFail.reverting(fn(rhs, lhs));
+  }
+
   describe('add', function () {
-    it('adds correctly if it does not overflow and the result is positve', async function () {
+    it('adds correctly if it does not overflow and the result is positive', async function () {
       const a = new BN('1234');
       const b = new BN('5678');
 
-      (await this.safeMath.add(a, b)).should.be.bignumber.equal(a.add(b));
+      await testCommutative(this.safeMath.add, a, b, a.add(b));
     });
 
     it('adds correctly if it does not overflow and the result is negative', async function () {
       const a = MAX_INT256;
       const b = MIN_INT256;
 
-      const result = await this.safeMath.add(a, b);
-      result.should.be.bignumber.equal(a.add(b));
+      await testCommutative(this.safeMath.add, a, b, a.add(b));
     });
 
     it('reverts on positive addition overflow', async function () {
       const a = MAX_INT256;
       const b = new BN('1');
 
-      await shouldFail.reverting(this.safeMath.add(a, b));
+      await testFailsCommutative(this.safeMath.add, a, b);
     });
 
     it('reverts on negative addition overflow', async function () {
       const a = MIN_INT256;
       const b = new BN('-1');
 
-      await shouldFail.reverting(this.safeMath.add(a, b));
+      await testFailsCommutative(this.safeMath.add, a, b);
     });
   });
 
@@ -76,37 +85,28 @@ contract('SignedSafeMath', function () {
       const a = new BN('5678');
       const b = new BN('-1234');
 
-      const result = await this.safeMath.mul(a, b);
-      result.should.be.bignumber.equal(a.mul(b));
+      await testCommutative(this.safeMath.mul, a, b, a.mul(b));
     });
 
-    it('handles a zero product correctly', async function () {
+    it('multiplies by zero correctly', async function () {
       const a = new BN('0');
       const b = new BN('5678');
 
-      const result = await this.safeMath.mul(a, b);
-      result.should.be.bignumber.equal(a.mul(b));
+      await testCommutative(this.safeMath.mul, a, b, '0');
     });
 
     it('reverts on multiplication overflow, positive operands', async function () {
       const a = MAX_INT256;
       const b = new BN('2');
 
-      await shouldFail.reverting(this.safeMath.mul(a, b));
+      await testFailsCommutative(this.safeMath.mul, a, b);
     });
 
     it('reverts when minimum integer is multiplied by -1', async function () {
       const a = MIN_INT256;
       const b = new BN('-1');
 
-      await shouldFail.reverting(this.safeMath.mul(a, b));
-    });
-
-    it('reverts when -1 is multiplied by minimum integer', async function () {
-      const a = new BN('-1');
-      const b = MIN_INT256;
-
-      await shouldFail.reverting(this.safeMath.mul(a, b));
+      await testFailsCommutative(this.safeMath.mul, a, b);
     });
   });
 
@@ -119,7 +119,21 @@ contract('SignedSafeMath', function () {
       result.should.be.bignumber.equal(a.div(b));
     });
 
-    it('reverts on zero division', async function () {
+    it('divides zero correctly', async function () {
+      const a = new BN('0');
+      const b = new BN('5678');
+
+      (await this.safeMath.div(a, b)).should.be.bignumber.equal('0');
+    });
+
+    it('returns complete number result on non-even division', async function () {
+      const a = new BN('7000');
+      const b = new BN('5678');
+
+      (await this.safeMath.div(a, b)).should.be.bignumber.equal('1');
+    });
+
+    it('reverts on division by zero', async function () {
       const a = new BN('-5678');
       const b = new BN('0');
 

test/helpers/sign.js

@@ -9,9 +9,21 @@ function toEthSignedMessageHash (messageHex) {
   return web3.utils.sha3(Buffer.concat([prefix, messageBuffer]));
 }
 
+function fixSignature (signature) {
+  // in geth its always 27/28, in ganache its 0/1. Change to 27/28 to prevent
+  // signature malleability if version is 0/1
+  // see https://github.com/ethereum/go-ethereum/blob/v1.8.23/internal/ethapi/api.go#L465
+  let v = parseInt(signature.slice(130, 132), 16);
+  if (v < 27) {
+    v += 27;
+  }
+  const vHex = v.toString(16);
+  return signature.slice(0, 130) + vHex;
+}
+
 // signs message in node (ganache auto-applies "Ethereum Signed Message" prefix)
-const signMessage = (signer, messageHex = '0x') => {
-  return web3.eth.sign(messageHex, signer);
+async function signMessage (signer, messageHex = '0x') {
+  return fixSignature(await web3.eth.sign(messageHex, signer));
 };
 
 /**
@@ -50,5 +62,6 @@ const getSignFor = (contract, signer) => (redeemer, methodName, methodArgs = [])
 module.exports = {
   signMessage,
   toEthSignedMessageHash,
+  fixSignature,
   getSignFor,
 };

test/lifecycle/Pausable.test.js

@@ -17,7 +17,7 @@ contract('Pausable', function ([_, pauser, otherPauser, anyone, ...otherAccounts
     shouldBehaveLikePublicRole(pauser, otherPauser, otherAccounts, 'pauser');
   });
 
-  context('when unapused', function () {
+  context('when unpaused', function () {
     beforeEach(async function () {
       (await this.pausable.paused()).should.equal(false);
     });

test/math/SafeMath.test.js

@@ -8,19 +8,29 @@ contract('SafeMath', function () {
     this.safeMath = await SafeMathMock.new();
   });
 
+  async function testCommutative (fn, lhs, rhs, expected) {
+    (await fn(lhs, rhs)).should.be.bignumber.equal(expected);
+    (await fn(rhs, lhs)).should.be.bignumber.equal(expected);
+  }
+
+  async function testFailsCommutative (fn, lhs, rhs) {
+    await shouldFail.reverting(fn(lhs, rhs));
+    await shouldFail.reverting(fn(rhs, lhs));
+  }
+
   describe('add', function () {
     it('adds correctly', async function () {
       const a = new BN('5678');
       const b = new BN('1234');
 
-      (await this.safeMath.add(a, b)).should.be.bignumber.equal(a.add(b));
+      await testCommutative(this.safeMath.add, a, b, a.add(b));
     });
 
     it('reverts on addition overflow', async function () {
       const a = MAX_UINT256;
       const b = new BN('1');
 
-      await shouldFail.reverting(this.safeMath.add(a, b));
+      await testFailsCommutative(this.safeMath.add, a, b);
     });
   });
 
@@ -45,28 +55,21 @@ contract('SafeMath', function () {
       const a = new BN('1234');
       const b = new BN('5678');
 
-      (await this.safeMath.mul(a, b)).should.be.bignumber.equal(a.mul(b));
+      await testCommutative(this.safeMath.mul, a, b, a.mul(b));
     });
 
-    it('handles a zero product correctly (first number as zero)', async function () {
+    it('multiplies by zero correctly', async function () {
       const a = new BN('0');
       const b = new BN('5678');
 
-      (await this.safeMath.mul(a, b)).should.be.bignumber.equal(a.mul(b));
-    });
-
-    it('handles a zero product correctly (second number as zero)', async function () {
-      const a = new BN('5678');
-      const b = new BN('0');
-
-      (await this.safeMath.mul(a, b)).should.be.bignumber.equal(a.mul(b));
+      await testCommutative(this.safeMath.mul, a, b, '0');
     });
 
     it('reverts on multiplication overflow', async function () {
       const a = MAX_UINT256;
       const b = new BN('2');
 
-      await shouldFail.reverting(this.safeMath.mul(a, b));
+      await testFailsCommutative(this.safeMath.mul, a, b);
     });
   });
 
@@ -92,7 +95,7 @@ contract('SafeMath', function () {
       (await this.safeMath.div(a, b)).should.be.bignumber.equal('1');
     });
 
-    it('reverts on zero division', async function () {
+    it('reverts on divison by zero', async function () {
       const a = new BN('5678');
       const b = new BN('0');
 

test/ownership/Ownable.behavior.js

@@ -16,7 +16,7 @@ function shouldBehaveLikeOwnable (owner, [anyone]) {
       (await this.ownable.isOwner({ from: anyone })).should.be.equal(true);
     });
 
-    it('should prevent non-owners from transfering', async function () {
+    it('should prevent non-owners from transferring', async function () {
       await shouldFail.reverting(this.ownable.transferOwnership(anyone, { from: anyone }));
     });
 

test/ownership/Secondary.test.js

@@ -29,7 +29,7 @@ contract('Secondary', function ([_, primary, newPrimary, anyone]) {
       (await this.secondary.primary()).should.equal(newPrimary);
     });
 
-    it('reverts when transfering to the null address', async function () {
+    it('reverts when transferring to the null address', async function () {
       await shouldFail.reverting(this.secondary.transferPrimary(ZERO_ADDRESS, { from: primary }));
     });
 

test/payment/PaymentSplitter.test.js

@@ -84,19 +84,19 @@ contract('PaymentSplitter', function ([_, owner, payee1, payee2, payee3, nonpaye
       const initAmount1 = await balance.current(payee1);
       const { logs: logs1 } = await this.contract.release(payee1, { gasPrice: 0 });
       const profit1 = (await balance.current(payee1)).sub(initAmount1);
-      profit1.should.be.bignumber.equal(ether('0.20', 'ether'));
+      profit1.should.be.bignumber.equal(ether('0.20'));
       expectEvent.inLogs(logs1, 'PaymentReleased', { to: payee1, amount: profit1 });
 
       const initAmount2 = await balance.current(payee2);
       const { logs: logs2 } = await this.contract.release(payee2, { gasPrice: 0 });
       const profit2 = (await balance.current(payee2)).sub(initAmount2);
-      profit2.should.be.bignumber.equal(ether('0.10', 'ether'));
+      profit2.should.be.bignumber.equal(ether('0.10'));
       expectEvent.inLogs(logs2, 'PaymentReleased', { to: payee2, amount: profit2 });
 
       const initAmount3 = await balance.current(payee3);
       const { logs: logs3 } = await this.contract.release(payee3, { gasPrice: 0 });
       const profit3 = (await balance.current(payee3)).sub(initAmount3);
-      profit3.should.be.bignumber.equal(ether('0.70', 'ether'));
+      profit3.should.be.bignumber.equal(ether('0.70'));
       expectEvent.inLogs(logs3, 'PaymentReleased', { to: payee3, amount: profit3 });
 
       // end balance should be zero

test/token/ERC20/ERC20.test.js

@@ -73,89 +73,6 @@ contract('ERC20', function ([_, initialHolder, recipient, anotherAccount]) {
     });
   });
 
-  describe('approve', function () {
-    describe('when the spender is not the zero address', function () {
-      const spender = recipient;
-
-      describe('when the sender has enough balance', function () {
-        const amount = initialSupply;
-
-        it('emits an approval event', async function () {
-          const { logs } = await this.token.approve(spender, amount, { from: initialHolder });
-
-          expectEvent.inLogs(logs, 'Approval', {
-            owner: initialHolder,
-            spender: spender,
-            value: amount,
-          });
-        });
-
-        describe('when there was no approved amount before', function () {
-          it('approves the requested amount', async function () {
-            await this.token.approve(spender, amount, { from: initialHolder });
-
-            (await this.token.allowance(initialHolder, spender)).should.be.bignumber.equal(amount);
-          });
-        });
-
-        describe('when the spender had an approved amount', function () {
-          beforeEach(async function () {
-            await this.token.approve(spender, new BN(1), { from: initialHolder });
-          });
-
-          it('approves the requested amount and replaces the previous one', async function () {
-            await this.token.approve(spender, amount, { from: initialHolder });
-
-            (await this.token.allowance(initialHolder, spender)).should.be.bignumber.equal(amount);
-          });
-        });
-      });
-
-      describe('when the sender does not have enough balance', function () {
-        const amount = initialSupply.addn(1);
-
-        it('emits an approval event', async function () {
-          const { logs } = await this.token.approve(spender, amount, { from: initialHolder });
-
-          expectEvent.inLogs(logs, 'Approval', {
-            owner: initialHolder,
-            spender: spender,
-            value: amount,
-          });
-        });
-
-        describe('when there was no approved amount before', function () {
-          it('approves the requested amount', async function () {
-            await this.token.approve(spender, amount, { from: initialHolder });
-
-            (await this.token.allowance(initialHolder, spender)).should.be.bignumber.equal(amount);
-          });
-        });
-
-        describe('when the spender had an approved amount', function () {
-          beforeEach(async function () {
-            await this.token.approve(spender, new BN(1), { from: initialHolder });
-          });
-
-          it('approves the requested amount and replaces the previous one', async function () {
-            await this.token.approve(spender, amount, { from: initialHolder });
-
-            (await this.token.allowance(initialHolder, spender)).should.be.bignumber.equal(amount);
-          });
-        });
-      });
-    });
-
-    describe('when the spender is the zero address', function () {
-      const amount = initialSupply;
-      const spender = ZERO_ADDRESS;
-
-      it('reverts', async function () {
-        await shouldFail.reverting(this.token.approve(spender, amount, { from: initialHolder }));
-      });
-    });
-  });
-
   describe('transfer from', function () {
     const spender = recipient;
 
@@ -546,4 +463,100 @@ contract('ERC20', function ([_, initialHolder, recipient, anotherAccount]) {
       describeBurnFrom('for less amount than allowance', allowance.subn(1));
     });
   });
+
+  describe('approve', function () {
+    testApprove(initialHolder, recipient, initialSupply, function (owner, spender, amount) {
+      return this.token.approve(spender, amount, { from: owner });
+    });
+  });
+
+  describe('_approve', function () {
+    testApprove(initialHolder, recipient, initialSupply, function (owner, spender, amount) {
+      return this.token.approveInternal(owner, spender, amount);
+    });
+
+    describe('when the owner is the zero address', function () {
+      it('reverts', async function () {
+        await shouldFail.reverting(this.token.approveInternal(ZERO_ADDRESS, recipient, initialSupply));
+      });
+    });
+  });
+
+  function testApprove (owner, spender, supply, approve) {
+    describe('when the spender is not the zero address', function () {
+      describe('when the sender has enough balance', function () {
+        const amount = supply;
+
+        it('emits an approval event', async function () {
+          const { logs } = await approve.call(this, owner, spender, amount);
+
+          expectEvent.inLogs(logs, 'Approval', {
+            owner: owner,
+            spender: spender,
+            value: amount,
+          });
+        });
+
+        describe('when there was no approved amount before', function () {
+          it('approves the requested amount', async function () {
+            await approve.call(this, owner, spender, amount);
+
+            (await this.token.allowance(owner, spender)).should.be.bignumber.equal(amount);
+          });
+        });
+
+        describe('when the spender had an approved amount', function () {
+          beforeEach(async function () {
+            await approve.call(this, owner, spender, new BN(1));
+          });
+
+          it('approves the requested amount and replaces the previous one', async function () {
+            await approve.call(this, owner, spender, amount);
+
+            (await this.token.allowance(owner, spender)).should.be.bignumber.equal(amount);
+          });
+        });
+      });
+
+      describe('when the sender does not have enough balance', function () {
+        const amount = supply.addn(1);
+
+        it('emits an approval event', async function () {
+          const { logs } = await approve.call(this, owner, spender, amount);
+
+          expectEvent.inLogs(logs, 'Approval', {
+            owner: owner,
+            spender: spender,
+            value: amount,
+          });
+        });
+
+        describe('when there was no approved amount before', function () {
+          it('approves the requested amount', async function () {
+            await approve.call(this, owner, spender, amount);
+
+            (await this.token.allowance(owner, spender)).should.be.bignumber.equal(amount);
+          });
+        });
+
+        describe('when the spender had an approved amount', function () {
+          beforeEach(async function () {
+            await approve.call(this, owner, spender, new BN(1));
+          });
+
+          it('approves the requested amount and replaces the previous one', async function () {
+            await approve.call(this, owner, spender, amount);
+
+            (await this.token.allowance(owner, spender)).should.be.bignumber.equal(amount);
+          });
+        });
+      });
+    });
+
+    describe('when the spender is the zero address', function () {
+      it('reverts', async function () {
+        await shouldFail.reverting(approve.call(this, owner, ZERO_ADDRESS, supply));
+      });
+    });
+  }
 });

test/token/ERC20/SafeERC20.test.js

 const { shouldFail } = require('openzeppelin-test-helpers');
 
-const SafeERC20Helper = artifacts.require('SafeERC20Helper');
+const ERC20ReturnFalseMock = artifacts.require('ERC20ReturnFalseMock');
+const ERC20ReturnTrueMock = artifacts.require('ERC20ReturnTrueMock');
+const ERC20NoReturnMock = artifacts.require('ERC20NoReturnMock');
+const SafeERC20Wrapper = artifacts.require('SafeERC20Wrapper');
 
-contract('SafeERC20', function () {
+contract('SafeERC20', function ([_, hasNoCode]) {
+  describe('with address that has no contract code', function () {
     beforeEach(async function () {
-    this.helper = await SafeERC20Helper.new();
+      this.wrapper = await SafeERC20Wrapper.new(hasNoCode);
+    });
+
+    shouldRevertOnAllCalls();
   });
 
   describe('with token that returns false on all calls', function () {
+    beforeEach(async function () {
+      this.wrapper = await SafeERC20Wrapper.new((await ERC20ReturnFalseMock.new()).address);
+    });
+
+    shouldRevertOnAllCalls();
+  });
+
+  describe('with token that returns true on all calls', function () {
+    beforeEach(async function () {
+      this.wrapper = await SafeERC20Wrapper.new((await ERC20ReturnTrueMock.new()).address);
+    });
+
+    shouldOnlyRevertOnErrors();
+  });
+
+  describe('with token that returns no boolean values', function () {
+    beforeEach(async function () {
+      this.wrapper = await SafeERC20Wrapper.new((await ERC20NoReturnMock.new()).address);
+    });
+
+    shouldOnlyRevertOnErrors();
+  });
+});
+
+function shouldRevertOnAllCalls () {
   it('reverts on transfer', async function () {
-      await shouldFail.reverting(this.helper.doFailingTransfer());
+    await shouldFail.reverting(this.wrapper.transfer());
   });
 
   it('reverts on transferFrom', async function () {
-      await shouldFail.reverting(this.helper.doFailingTransferFrom());
+    await shouldFail.reverting(this.wrapper.transferFrom());
   });
 
   it('reverts on approve', async function () {
-      await shouldFail.reverting(this.helper.doFailingApprove());
+    await shouldFail.reverting(this.wrapper.approve(0));
   });
 
   it('reverts on increaseAllowance', async function () {
-      await shouldFail.reverting(this.helper.doFailingIncreaseAllowance());
+    await shouldFail.reverting(this.wrapper.increaseAllowance(0));
   });
 
   it('reverts on decreaseAllowance', async function () {
-      await shouldFail.reverting(this.helper.doFailingDecreaseAllowance());
-    });
+    await shouldFail.reverting(this.wrapper.decreaseAllowance(0));
   });
+}
 
-  describe('with token that returns true on all calls', function () {
+function shouldOnlyRevertOnErrors () {
   it('doesn\'t revert on transfer', async function () {
-      await this.helper.doSucceedingTransfer();
+    await this.wrapper.transfer();
   });
 
   it('doesn\'t revert on transferFrom', async function () {
-      await this.helper.doSucceedingTransferFrom();
+    await this.wrapper.transferFrom();
   });
 
   describe('approvals', function () {
     context('with zero allowance', function () {
       beforeEach(async function () {
-          await this.helper.setAllowance(0);
+        await this.wrapper.setAllowance(0);
       });
 
       it('doesn\'t revert when approving a non-zero allowance', async function () {
-          await this.helper.doSucceedingApprove(100);
+        await this.wrapper.approve(100);
       });
 
       it('doesn\'t revert when approving a zero allowance', async function () {
-          await this.helper.doSucceedingApprove(0);
+        await this.wrapper.approve(0);
       });
 
       it('doesn\'t revert when increasing the allowance', async function () {
-          await this.helper.doSucceedingIncreaseAllowance(10);
+        await this.wrapper.increaseAllowance(10);
       });
 
       it('reverts when decreasing the allowance', async function () {
-          await shouldFail.reverting(this.helper.doSucceedingDecreaseAllowance(10));
+        await shouldFail.reverting(this.wrapper.decreaseAllowance(10));
       });
     });
 
     context('with non-zero allowance', function () {
       beforeEach(async function () {
-          await this.helper.setAllowance(100);
+        await this.wrapper.setAllowance(100);
       });
 
       it('reverts when approving a non-zero allowance', async function () {
-          await shouldFail.reverting(this.helper.doSucceedingApprove(20));
+        await shouldFail.reverting(this.wrapper.approve(20));
       });
 
       it('doesn\'t revert when approving a zero allowance', async function () {
-          await this.helper.doSucceedingApprove(0);
+        await this.wrapper.approve(0);
       });
 
       it('doesn\'t revert when increasing the allowance', async function () {
-          await this.helper.doSucceedingIncreaseAllowance(10);
+        await this.wrapper.increaseAllowance(10);
       });
 
       it('doesn\'t revert when decreasing the allowance to a positive value', async function () {
-          await this.helper.doSucceedingDecreaseAllowance(50);
+        await this.wrapper.decreaseAllowance(50);
       });
 
       it('reverts when decreasing the allowance to a negative value', async function () {
-          await shouldFail.reverting(this.helper.doSucceedingDecreaseAllowance(200));
+        await shouldFail.reverting(this.wrapper.decreaseAllowance(200));
       });
     });
   });
-  });
-});
+}

test/token/ERC721/ERC721PausedToken.behavior.js

@@ -55,7 +55,7 @@ function shouldBehaveLikeERC721PausedToken (owner, [recipient, operator]) {
     });
 
     describe('exists', function () {
-      it('should return token existance', async function () {
+      it('should return token existence', async function () {
         (await this.token.exists(firstTokenId)).should.equal(true);
       });
     });

truffle-config.js

@@ -16,7 +16,7 @@ module.exports = {
 
   compilers: {
     solc: {
-      version: '0.5.0',
+      version: '0.5.2',
     },
   },
 };