Add ERC20 compatibility to ERC777. (#1735)

* Add ERC20 compatibility.

* Reusing ERC20 tests for ERC777.

* Improve documentation.

* Add changelog entry.

* Improved ERC20 behavior tests.

* Add revert reasons to ERC777.

* ERC20 methods allow sending tokens to contracts with no interface.

* Register ERC20 interface.

* Add comment about avoidLockingTokens.

* Improve revert reason string.

* Make ERC777 implement IERC20.

* Fix test revert string.

* Remove unnecesary require.

* Add private _transfer.

* Update contracts/drafts/ERC777/ERC777.sol

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Update private helper names.

(cherry picked from commit aa4c9fea)

CHANGELOG.md

@@ -4,7 +4,7 @@
 
 ### New features:
  * `ERC1820`: added support for interacting with the [ERC1820](https://eips.ethereum.org/EIPS/eip-1820) registry contract (`IERC1820Registry`), as well as base contracts that can be registered as implementers there. ([#1677](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1677))
- * `ERC777`: initial support for the [ERC777 token](https://eips.ethereum.org/EIPS/eip-777), which has multiple improvements over `ERC20` such as built-in burning, a more  straightforward permission system, and optional sender and receiver hooks on transfer (mandatory for contracts!). ([#1684](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1684))
+ * `ERC777`: support for the [ERC777 token](https://eips.ethereum.org/EIPS/eip-777), which has multiple improvements over `ERC20` (but is backwards compatible with it) such as built-in burning, a more  straightforward permission system, and optional sender and receiver hooks on transfer (mandatory for contracts!). ([#1684](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1684))
  * All contracts now have revert reason strings, which give insight into error conditions, and help debug failing transactions. ([#1704](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1704))
 
 ### Improvements:

contracts/drafts/ERC777/ERC777.sol

@@ -3,6 +3,7 @@ pragma solidity ^0.5.0;
 import "./IERC777.sol";
 import "./IERC777Recipient.sol";
 import "./IERC777Sender.sol";
+import "../../token/ERC20/IERC20.sol";
 import "../../math/SafeMath.sol";
 import "../../utils/Address.sol";
 import "../IERC1820Registry.sol";
@@ -11,20 +12,19 @@ import "../IERC1820Registry.sol";
  * @title ERC777 token implementation, with granularity harcoded to 1.
  * @author etsvigun <utgarda@gmail.com>, Bertrand Masius <github@catageeks.tk>
  */
-contract ERC777 is IERC777 {
+contract ERC777 is IERC777, IERC20 {
     using SafeMath for uint256;
     using Address for address;
 
     IERC1820Registry private _erc1820 = IERC1820Registry(0x1820a4B7618BdE71Dce8cdc73aAB6C95905faD24);
 
-    string private _name;
-
-    string private _symbol;
-
     mapping(address => uint256) private _balances;
 
     uint256 private _totalSupply;
 
+    string private _name;
+    string private _symbol;
+
     bytes32 constant private TOKENS_SENDER_INTERFACE_HASH = keccak256("ERC777TokensSender");
     bytes32 constant private TOKENS_RECIPIENT_INTERFACE_HASH = keccak256("ERC777TokensRecipient");
 
@@ -38,6 +38,9 @@ contract ERC777 is IERC777 {
     mapping(address => mapping(address => bool)) private _operators;
     mapping(address => mapping(address => bool)) private _revokedDefaultOperators;
 
+    // ERC20-allowances
+    mapping (address => mapping (address => uint256)) private _allowances;
+
     constructor(
         string memory name,
         string memory symbol,
@@ -51,8 +54,9 @@ contract ERC777 is IERC777 {
             _defaultOperators[_defaultOperatorsArray[i]] = true;
         }
 
-        // register interface
+        // register interfaces
         _erc1820.setInterfaceImplementer(address(this), keccak256("ERC777Token"), address(this));
+        _erc1820.setInterfaceImplementer(address(this), keccak256("ERC20Token"), address(this));
     }
 
     /**
@@ -62,7 +66,7 @@ contract ERC777 is IERC777 {
      * @param data bytes information attached to the send, and intended for the recipient (to)
      */
     function send(address to, uint256 amount, bytes calldata data) external {
-        _send(msg.sender, msg.sender, to, amount, data, "");
+        _sendRequiringReceptionAck(msg.sender, msg.sender, to, amount, data, "");
     }
 
     /**
@@ -82,8 +86,36 @@ contract ERC777 is IERC777 {
     )
     external
     {
-        require(isOperatorFor(msg.sender, from));
-        _send(msg.sender, from, to, amount, data, operatorData);
+        require(isOperatorFor(msg.sender, from), "ERC777: caller is not an operator for holder");
+        _sendRequiringReceptionAck(msg.sender, from, to, amount, data, operatorData);
+    }
+
+    /**
+     * @dev Transfer token to a specified address.
+     * Required for ERC20 compatiblity. Note that transferring tokens this way may result in locked tokens (i.e. tokens
+     * can be sent to a contract that does not implement the ERC777TokensRecipient interface).
+     * @param to The address to transfer to.
+     * @param value The amount to be transferred.
+     */
+    function transfer(address to, uint256 value) external returns (bool) {
+        _transfer(msg.sender, msg.sender, to, value);
+        return true;
+    }
+
+    /**
+     * @dev Transfer tokens from one address to another.
+     * Note that while this function emits an Approval event, this is not required as per the specification,
+     * and other compliant implementations may not emit the event.
+     * Required for ERC20 compatiblity. Note that transferring tokens this way may result in locked tokens (i.e. tokens
+     * can be sent to a contract that does not implement the ERC777TokensRecipient interface).
+     * @param from address The address which you want to send tokens from
+     * @param to address The address which you want to transfer to
+     * @param value uint256 the amount of tokens to be transferred
+     */
+    function transferFrom(address from, address to, uint256 value) external returns (bool) {
+        _transfer(msg.sender, from, to, value);
+        _approve(from, msg.sender, _allowances[from][msg.sender].sub(value));
+        return true;
     }
 
     /**
@@ -103,7 +135,7 @@ contract ERC777 is IERC777 {
      * @param operatorData bytes extra information provided by the operator (if any)
      */
     function operatorBurn(address from, uint256 amount, bytes calldata data, bytes calldata operatorData) external {
-        require(isOperatorFor(msg.sender, from));
+        require(isOperatorFor(msg.sender, from), "ERC777: caller is not an operator for holder");
         _burn(msg.sender, from, amount, data, operatorData);
     }
 
@@ -112,7 +144,7 @@ contract ERC777 is IERC777 {
      * @param operator address to be authorized as operator
      */
     function authorizeOperator(address operator) external {
-        require(msg.sender != operator);
+        require(msg.sender != operator, "ERC777: authorizing self as operator");
 
         if (_defaultOperators[operator]) {
             delete _revokedDefaultOperators[msg.sender][operator];
@@ -128,7 +160,7 @@ contract ERC777 is IERC777 {
      * @param operator address to revoke operator rights from
      */
     function revokeOperator(address operator) external {
-        require(operator != msg.sender);
+        require(operator != msg.sender, "ERC777: revoking self as operator");
 
         if (_defaultOperators[operator]) {
             _revokedDefaultOperators[msg.sender][operator] = true;
@@ -140,17 +172,18 @@ contract ERC777 is IERC777 {
     }
 
     /**
-     * @return the name of the token.
-     */
-    function name() public view returns (string memory) {
-        return _name;
-    }
-
-    /**
-     * @return the symbol of the token.
+     * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
+     * Beware that changing an allowance with this method brings the risk that someone may use both the old
+     * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
+     * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
+     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
+     * Required for ERC20 compatilibity.
+     * @param spender The address which will spend the funds.
+     * @param value The amount of tokens to be spent.
      */
-    function symbol() public view returns (string memory) {
-        return _symbol;
+    function approve(address spender, uint256 value) external returns (bool) {
+        _approve(msg.sender, spender, value);
+        return true;
     }
 
     /**
@@ -170,6 +203,27 @@ contract ERC777 is IERC777 {
     }
 
     /**
+     * @return the name of the token.
+     */
+    function name() public view returns (string memory) {
+        return _name;
+    }
+
+    /**
+     * @return the symbol of the token.
+     */
+    function symbol() public view returns (string memory) {
+        return _symbol;
+    }
+
+    /**
+     * @return the number of decimals of the token.
+     */
+    function decimals() public pure returns (uint8) {
+        return 18; // The spec requires that decimals be 18
+    }
+
+    /**
      * @dev Gets the token's granularity,
      * i.e. the smallest number of tokens (in the basic unit)
      * which may be minted, sent or burned at any time
@@ -204,6 +258,17 @@ contract ERC777 is IERC777 {
     }
 
     /**
+     * @dev Function to check the amount of tokens that an owner allowed to a spender.
+     * Required for ERC20 compatibility.
+     * @param owner address The address which owns the funds.
+     * @param spender address The address which will spend the funds.
+     * @return A uint256 specifying the amount of tokens still available for the spender.
+     */
+    function allowance(address owner, address spender) public view returns (uint256) {
+        return _allowances[owner][spender];
+    }
+
+    /**
      * @dev Mint tokens. Does not check authorization of operator
      * @dev the caller may ckeck that operator is authorized before calling
      * @param operator address operator requesting the operation
@@ -221,15 +286,42 @@ contract ERC777 is IERC777 {
     )
     internal
     {
-        require(to != address(0));
+        require(to != address(0), "ERC777: mint to the zero address");
 
         // Update state variables
         _totalSupply = _totalSupply.add(amount);
         _balances[to] = _balances[to].add(amount);
 
-        _callTokensReceived(operator, address(0), to, amount, userData, operatorData);
+        _callTokensReceived(operator, address(0), to, amount, userData, operatorData, true);
 
         emit Minted(operator, to, amount, userData, operatorData);
+        emit Transfer(address(0), to, amount);
+    }
+
+    function _transfer(address operator, address from, address to, uint256 amount) private {
+        _sendAllowingNoReceptionAck(operator, from, to, amount, "", "");
+    }
+
+    function _sendRequiringReceptionAck(
+        address operator,
+        address from,
+        address to,
+        uint256 amount,
+        bytes memory userData,
+        bytes memory operatorData
+    ) private {
+        _send(operator, from, to, amount, userData, operatorData, true);
+    }
+
+    function _sendAllowingNoReceptionAck(
+        address operator,
+        address from,
+        address to,
+        uint256 amount,
+        bytes memory userData,
+        bytes memory operatorData
+    ) private {
+        _send(operator, from, to, amount, userData, operatorData, false);
     }
 
     /**
@@ -240,6 +332,7 @@ contract ERC777 is IERC777 {
      * @param amount uint256 amount of tokens to transfer
      * @param userData bytes extra information provided by the token holder (if any)
      * @param operatorData bytes extra information provided by the operator (if any)
+     * @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
      */
     function _send(
         address operator,
@@ -247,12 +340,13 @@ contract ERC777 is IERC777 {
         address to,
         uint256 amount,
         bytes memory userData,
-        bytes memory operatorData
+        bytes memory operatorData,
+        bool requireReceptionAck
     )
     private
     {
-        require(from != address(0));
-        require(to != address(0));
+        require(from != address(0), "ERC777: transfer from the zero address");
+        require(to != address(0), "ERC777: transfer to the zero address");
 
         _callTokensToSend(operator, from, to, amount, userData, operatorData);
 
@@ -260,9 +354,10 @@ contract ERC777 is IERC777 {
         _balances[from] = _balances[from].sub(amount);
         _balances[to] = _balances[to].add(amount);
 
-        _callTokensReceived(operator, from, to, amount, userData, operatorData);
+        _callTokensReceived(operator, from, to, amount, userData, operatorData, requireReceptionAck);
 
         emit Sent(operator, from, to, amount, userData, operatorData);
+        emit Transfer(from, to, amount);
     }
 
     /**
@@ -282,7 +377,7 @@ contract ERC777 is IERC777 {
     )
     private
     {
-        require(from != address(0));
+        require(from != address(0), "ERC777: burn from the zero address");
 
         _callTokensToSend(operator, from, address(0), amount, data, operatorData);
 
@@ -291,6 +386,17 @@ contract ERC777 is IERC777 {
         _balances[from] = _balances[from].sub(amount);
 
         emit Burned(operator, from, amount, data, operatorData);
+        emit Transfer(from, address(0), amount);
+    }
+
+    function _approve(address owner, address spender, uint256 value) private {
+        // TODO: restore this require statement if this function becomes internal, or is called at a new callsite. It is
+        // currently unnecessary.
+        //require(owner != address(0), "ERC777: approve from the zero address");
+        require(spender != address(0), "ERC777: approve to the zero address");
+
+        _allowances[owner][spender] = value;
+        emit Approval(owner, spender, value);
     }
 
     /**
@@ -327,6 +433,7 @@ contract ERC777 is IERC777 {
      * @param amount uint256 amount of tokens to transfer
      * @param userData bytes extra information provided by the token holder (if any)
      * @param operatorData bytes extra information provided by the operator (if any)
+     * @param requireReceptionAck if true, contract recipients are required to implement ERC777TokensRecipient
      */
     function _callTokensReceived(
         address operator,
@@ -334,15 +441,16 @@ contract ERC777 is IERC777 {
         address to,
         uint256 amount,
         bytes memory userData,
-        bytes memory operatorData
+        bytes memory operatorData,
+        bool requireReceptionAck
     )
     private
     {
         address implementer = _erc1820.getInterfaceImplementer(to, TOKENS_RECIPIENT_INTERFACE_HASH);
         if (implementer != address(0)) {
             IERC777Recipient(implementer).tokensReceived(operator, from, to, amount, userData, operatorData);
-        } else {
-            require(!to.isContract());
+        } else if (requireReceptionAck) {
+            require(!to.isContract(), "ERC777: token recipient contract has no implementer for ERC777TokensRecipient");
         }
     }
 }

contracts/token/ERC20/ERC20.sol

@@ -20,7 +20,7 @@ contract ERC20 is IERC20 {
 
     mapping (address => uint256) private _balances;
 
-    mapping (address => mapping (address => uint256)) private _allowed;
+    mapping (address => mapping (address => uint256)) private _allowances;
 
     uint256 private _totalSupply;
 
@@ -47,7 +47,7 @@ contract ERC20 is IERC20 {
      * @return A uint256 specifying the amount of tokens still available for the spender.
      */
     function allowance(address owner, address spender) public view returns (uint256) {
-        return _allowed[owner][spender];
+        return _allowances[owner][spender];
     }
 
     /**
@@ -84,13 +84,13 @@ contract ERC20 is IERC20 {
      */
     function transferFrom(address from, address to, uint256 value) public returns (bool) {
         _transfer(from, to, value);
-        _approve(from, msg.sender, _allowed[from][msg.sender].sub(value));
+        _approve(from, msg.sender, _allowances[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[msg.sender][spender] == 0. To increment
+     * approve should be called when _allowances[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
@@ -99,13 +99,13 @@ contract ERC20 is IERC20 {
      * @param addedValue The amount of tokens to increase the allowance by.
      */
     function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
-        _approve(msg.sender, spender, _allowed[msg.sender][spender].add(addedValue));
+        _approve(msg.sender, spender, _allowances[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[msg.sender][spender] == 0. To decrement
+     * approve should be called when _allowances[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
@@ -114,7 +114,7 @@ contract ERC20 is IERC20 {
      * @param subtractedValue The amount of tokens to decrease the allowance by.
      */
     function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
-        _approve(msg.sender, spender, _allowed[msg.sender][spender].sub(subtractedValue));
+        _approve(msg.sender, spender, _allowances[msg.sender][spender].sub(subtractedValue));
         return true;
     }
 
@@ -171,7 +171,7 @@ contract ERC20 is IERC20 {
         require(owner != address(0), "ERC20: approve from the zero address");
         require(spender != address(0), "ERC20: approve to the zero address");
 
-        _allowed[owner][spender] = value;
+        _allowances[owner][spender] = value;
         emit Approval(owner, spender, value);
     }
 
@@ -185,6 +185,6 @@ contract ERC20 is IERC20 {
      */
     function _burnFrom(address account, uint256 value) internal {
         _burn(account, value);
-        _approve(account, msg.sender, _allowed[account][msg.sender].sub(value));
+        _approve(account, msg.sender, _allowances[account][msg.sender].sub(value));
     }
 }

test/drafts/ERC777/ERC777.behavior.js

@@ -184,8 +184,9 @@ function shouldSendTokens (from, operator, to, amount, data, operatorData) {
     const initialFromBalance = await this.token.balanceOf(from);
     const initialToBalance = await this.token.balanceOf(to);
 
+    let logs;
     if (!operatorCall) {
-      const { logs } = await this.token.send(to, amount, data, { from });
+      ({ logs } = await this.token.send(to, amount, data, { from }));
       expectEvent.inLogs(logs, 'Sent', {
         operator: from,
         from,
@@ -195,7 +196,7 @@ function shouldSendTokens (from, operator, to, amount, data, operatorData) {
         operatorData: null,
       });
     } else {
-      const { logs } = await this.token.operatorSend(from, to, amount, data, operatorData, { from: operator });
+      ({ logs } = await this.token.operatorSend(from, to, amount, data, operatorData, { from: operator }));
       expectEvent.inLogs(logs, 'Sent', {
         operator,
         from,
@@ -206,6 +207,12 @@ function shouldSendTokens (from, operator, to, amount, data, operatorData) {
       });
     }
 
+    expectEvent.inLogs(logs, 'Transfer', {
+      from,
+      to,
+      value: amount,
+    });
+
     const finalTotalSupply = await this.token.totalSupply();
     const finalFromBalance = await this.token.balanceOf(from);
     const finalToBalance = await this.token.balanceOf(to);
@@ -231,8 +238,9 @@ function shouldBurnTokens (from, operator, amount, data, operatorData) {
     const initialTotalSupply = await this.token.totalSupply();
     const initialFromBalance = await this.token.balanceOf(from);
 
+    let logs;
     if (!operatorCall) {
-      const { logs } = await this.token.burn(amount, data, { from });
+      ({ logs } = await this.token.burn(amount, data, { from }));
       expectEvent.inLogs(logs, 'Burned', {
         operator: from,
         from,
@@ -241,7 +249,7 @@ function shouldBurnTokens (from, operator, amount, data, operatorData) {
         operatorData: null,
       });
     } else {
-      const { logs } = await this.token.operatorBurn(from, amount, data, operatorData, { from: operator });
+      ({ logs } = await this.token.operatorBurn(from, amount, data, operatorData, { from: operator }));
       expectEvent.inLogs(logs, 'Burned', {
         operator,
         from,
@@ -251,6 +259,12 @@ function shouldBurnTokens (from, operator, amount, data, operatorData) {
       });
     }
 
+    expectEvent.inLogs(logs, 'Transfer', {
+      from,
+      to: ZERO_ADDRESS,
+      value: amount,
+    });
+
     const finalTotalSupply = await this.token.totalSupply();
     const finalFromBalance = await this.token.balanceOf(from);
 
@@ -274,6 +288,7 @@ function shouldInternalMintTokens (operator, to, amount, data, operatorData) {
     const initialToBalance = await this.token.balanceOf(to);
 
     const { logs } = await this.token.mintInternal(operator, to, amount, data, operatorData);
+
     expectEvent.inLogs(logs, 'Minted', {
       operator,
       to,
@@ -282,6 +297,12 @@ function shouldInternalMintTokens (operator, to, amount, data, operatorData) {
       operatorData,
     });
 
+    expectEvent.inLogs(logs, 'Transfer', {
+      from: ZERO_ADDRESS,
+      to,
+      value: amount,
+    });
+
     const finalTotalSupply = await this.token.totalSupply();
     const finalToBalance = await this.token.balanceOf(to);
 

test/drafts/ERC777/ERC777.test.js

@@ -9,6 +9,10 @@ const {
   shouldBehaveLikeERC777SendBurnWithSendHook,
 } = require('./ERC777.behavior');
 
+const {
+  shouldBehaveLikeERC20,
+} = require('../../token/ERC20/ERC20.behavior');
+
 const ERC777 = artifacts.require('ERC777Mock');
 const ERC777SenderRecipientMock = artifacts.require('ERC777SenderRecipientMock');
 
@@ -32,6 +36,8 @@ contract('ERC777', function ([
       this.token = await ERC777.new(holder, initialSupply, name, symbol, defaultOperators);
     });
 
+    shouldBehaveLikeERC20('ERC777', initialSupply, holder, anyone, defaultOperatorA);
+
     it.skip('does not emit AuthorizedOperator events for default operators', async function () {
       expectEvent.not.inConstructor(this.token, 'AuthorizedOperator'); // This helper needs to be implemented
     });
@@ -45,7 +51,7 @@ contract('ERC777', function ([
         (await this.token.symbol()).should.equal(symbol);
       });
 
-      it('has a granularity of 1', async function () {
+      it('returns a granularity of 1', async function () {
         (await this.token.granularity()).should.be.bignumber.equal('1');
       });
 
@@ -59,14 +65,23 @@ contract('ERC777', function ([
         }
       });
 
-      it('returns thte total supply', async function () {
+      it('returns the total supply', async function () {
         (await this.token.totalSupply()).should.be.bignumber.equal(initialSupply);
       });
 
-      it('is registered in the registry', async function () {
+      it('returns 18 when decimals is called', async function () {
+        (await this.token.decimals()).should.be.bignumber.equal('18');
+      });
+
+      it('the ERC777Token interface is registered in the registry', async function () {
         (await this.erc1820.getInterfaceImplementer(this.token.address, web3.utils.soliditySha3('ERC777Token')))
           .should.equal(this.token.address);
       });
+
+      it('the ERC20Token interface is registered in the registry', async function () {
+        (await this.erc1820.getInterfaceImplementer(this.token.address, web3.utils.soliditySha3('ERC20Token')))
+          .should.equal(this.token.address);
+      });
     });
 
     describe('balanceOf', function () {
@@ -144,11 +159,15 @@ contract('ERC777', function ([
       });
 
       it('reverts when self-authorizing', async function () {
-        await shouldFail.reverting(this.token.authorizeOperator(holder, { from: holder }));
+        await shouldFail.reverting.withMessage(
+          this.token.authorizeOperator(holder, { from: holder }), 'ERC777: authorizing self as operator'
+        );
       });
 
       it('reverts when self-revoking', async function () {
-        await shouldFail.reverting(this.token.revokeOperator(holder, { from: holder }));
+        await shouldFail.reverting.withMessage(
+          this.token.revokeOperator(holder, { from: holder }), 'ERC777: revoking self as operator'
+        );
       });
 
       it('non-operators can be revoked', async function () {
@@ -209,7 +228,10 @@ contract('ERC777', function ([
         });
 
         it('cannot be revoked for themselves', async function () {
-          await shouldFail.reverting(this.token.revokeOperator(defaultOperatorA, { from: defaultOperatorA }));
+          await shouldFail.reverting.withMessage(
+            this.token.revokeOperator(defaultOperatorA, { from: defaultOperatorA }),
+            'ERC777: revoking self as operator'
+          );
         });
 
         context('with revoked default operator', function () {
@@ -259,20 +281,35 @@ contract('ERC777', function ([
             });
 
             it('send reverts', async function () {
-              await shouldFail.reverting(this.token.send(this.recipient, amount, data));
+              await shouldFail.reverting.withMessage(
+                this.token.send(this.recipient, amount, data, { from: holder }),
+                'ERC777: token recipient contract has no implementer for ERC777TokensRecipient',
+              );
             });
 
             it('operatorSend reverts', async function () {
-              await shouldFail.reverting(
-                this.token.operatorSend(this.sender, this.recipient, amount, data, operatorData, { from: operator })
+              await shouldFail.reverting.withMessage(
+                this.token.operatorSend(this.sender, this.recipient, amount, data, operatorData, { from: operator }),
+                'ERC777: token recipient contract has no implementer for ERC777TokensRecipient',
               );
             });
 
             it('mint (internal) reverts', async function () {
-              await shouldFail.reverting(
-                this.token.mintInternal(operator, this.recipient, amount, data, operatorData)
+              await shouldFail.reverting.withMessage(
+                this.token.mintInternal(operator, this.recipient, amount, data, operatorData),
+                'ERC777: token recipient contract has no implementer for ERC777TokensRecipient',
               );
             });
+
+            it('(ERC20) transfer succeeds', async function () {
+              await this.token.transfer(this.recipient, amount, { from: holder });
+            });
+
+            it('(ERC20) transferFrom succeeds', async function () {
+              const approved = anyone;
+              await this.token.approve(approved, amount, { from: this.sender });
+              await this.token.transferFrom(this.sender, this.recipient, amount, { from: approved });
+            });
           });
         });
 

test/token/ERC20/ERC20.behavior.js

+const { BN, constants, expectEvent, shouldFail } = require('openzeppelin-test-helpers');
+const { ZERO_ADDRESS } = constants;
+
+function shouldBehaveLikeERC20 (errorPrefix, initialSupply, initialHolder, recipient, anotherAccount) {
+  describe('total supply', function () {
+    it('returns the total amount of tokens', async function () {
+      (await this.token.totalSupply()).should.be.bignumber.equal(initialSupply);
+    });
+  });
+
+  describe('balanceOf', function () {
+    describe('when the requested account has no tokens', function () {
+      it('returns zero', async function () {
+        (await this.token.balanceOf(anotherAccount)).should.be.bignumber.equal('0');
+      });
+    });
+
+    describe('when the requested account has some tokens', function () {
+      it('returns the total amount of tokens', async function () {
+        (await this.token.balanceOf(initialHolder)).should.be.bignumber.equal(initialSupply);
+      });
+    });
+  });
+
+  describe('transfer', function () {
+    describe('when the recipient is not the zero address', function () {
+      const to = recipient;
+
+      describe('when the sender does not have enough balance', function () {
+        const amount = initialSupply.addn(1);
+
+        it('reverts', async function () {
+          await shouldFail.reverting.withMessage(this.token.transfer(to, amount, { from: initialHolder }),
+            'SafeMath: subtraction overflow'
+          );
+        });
+      });
+
+      describe('when the sender has enough balance', function () {
+        const amount = initialSupply;
+
+        it('transfers the requested amount', async function () {
+          await this.token.transfer(to, amount, { from: initialHolder });
+
+          (await this.token.balanceOf(initialHolder)).should.be.bignumber.equal('0');
+
+          (await this.token.balanceOf(to)).should.be.bignumber.equal(amount);
+        });
+
+        it('emits a transfer event', async function () {
+          const { logs } = await this.token.transfer(to, amount, { from: initialHolder });
+
+          expectEvent.inLogs(logs, 'Transfer', {
+            from: initialHolder,
+            to: to,
+            value: amount,
+          });
+        });
+      });
+    });
+
+    describe('when the recipient is the zero address', function () {
+      const to = ZERO_ADDRESS;
+
+      it('reverts', async function () {
+        await shouldFail.reverting.withMessage(this.token.transfer(to, initialSupply, { from: initialHolder }),
+          `${errorPrefix}: transfer to the zero address`
+        );
+      });
+    });
+  });
+
+  describe('transfer from', function () {
+    const spender = recipient;
+
+    describe('when the recipient is not the zero address', function () {
+      const to = anotherAccount;
+
+      describe('when the spender has enough approved balance', function () {
+        beforeEach(async function () {
+          await this.token.approve(spender, initialSupply, { from: initialHolder });
+        });
+
+        describe('when the initial holder has enough balance', function () {
+          const amount = initialSupply;
+
+          it('transfers the requested amount', async function () {
+            await this.token.transferFrom(initialHolder, to, amount, { from: spender });
+
+            (await this.token.balanceOf(initialHolder)).should.be.bignumber.equal('0');
+
+            (await this.token.balanceOf(to)).should.be.bignumber.equal(amount);
+          });
+
+          it('decreases the spender allowance', async function () {
+            await this.token.transferFrom(initialHolder, to, amount, { from: spender });
+
+            (await this.token.allowance(initialHolder, spender)).should.be.bignumber.equal('0');
+          });
+
+          it('emits a transfer event', async function () {
+            const { logs } = await this.token.transferFrom(initialHolder, to, amount, { from: spender });
+
+            expectEvent.inLogs(logs, 'Transfer', {
+              from: initialHolder,
+              to: to,
+              value: amount,
+            });
+          });
+
+          it('emits an approval event', async function () {
+            const { logs } = await this.token.transferFrom(initialHolder, to, amount, { from: spender });
+
+            expectEvent.inLogs(logs, 'Approval', {
+              owner: initialHolder,
+              spender: spender,
+              value: await this.token.allowance(initialHolder, spender),
+            });
+          });
+        });
+
+        describe('when the initial holder does not have enough balance', function () {
+          const amount = initialSupply.addn(1);
+
+          it('reverts', async function () {
+            await shouldFail.reverting.withMessage(this.token.transferFrom(
+              initialHolder, to, amount, { from: spender }), 'SafeMath: subtraction overflow'
+            );
+          });
+        });
+      });
+
+      describe('when the spender does not have enough approved balance', function () {
+        beforeEach(async function () {
+          await this.token.approve(spender, initialSupply.subn(1), { from: initialHolder });
+        });
+
+        describe('when the initial holder has enough balance', function () {
+          const amount = initialSupply;
+
+          it('reverts', async function () {
+            await shouldFail.reverting.withMessage(this.token.transferFrom(
+              initialHolder, to, amount, { from: spender }), 'SafeMath: subtraction overflow'
+            );
+          });
+        });
+
+        describe('when the initial holder does not have enough balance', function () {
+          const amount = initialSupply.addn(1);
+
+          it('reverts', async function () {
+            await shouldFail.reverting.withMessage(this.token.transferFrom(
+              initialHolder, to, amount, { from: spender }), 'SafeMath: subtraction overflow'
+            );
+          });
+        });
+      });
+    });
+
+    describe('when the recipient is the zero address', function () {
+      const amount = initialSupply;
+      const to = ZERO_ADDRESS;
+
+      beforeEach(async function () {
+        await this.token.approve(spender, amount, { from: initialHolder });
+      });
+
+      it('reverts', async function () {
+        await shouldFail.reverting.withMessage(this.token.transferFrom(
+          initialHolder, to, amount, { from: spender }), `${errorPrefix}: transfer to the zero address`
+        );
+      });
+    });
+  });
+
+  describe('approve', function () {
+    shouldBehaveLikeERC20Approve(errorPrefix, initialHolder, recipient, initialSupply,
+      function (owner, spender, amount) {
+        return this.token.approve(spender, amount, { from: owner });
+      }
+    );
+  });
+}
+
+function shouldBehaveLikeERC20Approve (errorPrefix, 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.withMessage(approve.call(this, owner, ZERO_ADDRESS, supply),
+        `${errorPrefix}: approve to the zero address`
+      );
+    });
+  });
+}
+
+module.exports = {
+  shouldBehaveLikeERC20,
+  shouldBehaveLikeERC20Approve,
+};

test/token/ERC20/ERC20.test.js

 const { BN, constants, expectEvent, shouldFail } = require('openzeppelin-test-helpers');
 const { ZERO_ADDRESS } = constants;
 
+const {
+  shouldBehaveLikeERC20,
+  shouldBehaveLikeERC20Approve,
+} = require('./ERC20.behavior');
+
 const ERC20Mock = artifacts.require('ERC20Mock');
 
 contract('ERC20', function ([_, initialHolder, recipient, anotherAccount]) {
   const initialSupply = new BN(100);
+
   beforeEach(async function () {
     this.token = await ERC20Mock.new(initialHolder, initialSupply);
   });
 
-  describe('total supply', function () {
-    it('returns the total amount of tokens', async function () {
-      (await this.token.totalSupply()).should.be.bignumber.equal(initialSupply);
-    });
-  });
-
-  describe('balanceOf', function () {
-    describe('when the requested account has no tokens', function () {
-      it('returns zero', async function () {
-        (await this.token.balanceOf(anotherAccount)).should.be.bignumber.equal('0');
-      });
-    });
-
-    describe('when the requested account has some tokens', function () {
-      it('returns the total amount of tokens', async function () {
-        (await this.token.balanceOf(initialHolder)).should.be.bignumber.equal(initialSupply);
-      });
-    });
-  });
-
-  describe('transfer', function () {
-    describe('when the recipient is not the zero address', function () {
-      const to = recipient;
-
-      describe('when the sender does not have enough balance', function () {
-        const amount = initialSupply.addn(1);
-
-        it('reverts', async function () {
-          await shouldFail.reverting.withMessage(this.token.transfer(to, amount, { from: initialHolder }),
-            'SafeMath: subtraction overflow'
-          );
-        });
-      });
-
-      describe('when the sender has enough balance', function () {
-        const amount = initialSupply;
-
-        it('transfers the requested amount', async function () {
-          await this.token.transfer(to, amount, { from: initialHolder });
-
-          (await this.token.balanceOf(initialHolder)).should.be.bignumber.equal('0');
-
-          (await this.token.balanceOf(to)).should.be.bignumber.equal(amount);
-        });
-
-        it('emits a transfer event', async function () {
-          const { logs } = await this.token.transfer(to, amount, { from: initialHolder });
-
-          expectEvent.inLogs(logs, 'Transfer', {
-            from: initialHolder,
-            to: to,
-            value: amount,
-          });
-        });
-      });
-    });
-
-    describe('when the recipient is the zero address', function () {
-      const to = ZERO_ADDRESS;
-
-      it('reverts', async function () {
-        await shouldFail.reverting.withMessage(this.token.transfer(to, initialSupply, { from: initialHolder }),
-          'ERC20: transfer to the zero address'
-        );
-      });
-    });
-  });
-
-  describe('transfer from', function () {
-    const spender = recipient;
-
-    describe('when the recipient is not the zero address', function () {
-      const to = anotherAccount;
-
-      describe('when the spender has enough approved balance', function () {
-        beforeEach(async function () {
-          await this.token.approve(spender, initialSupply, { from: initialHolder });
-        });
-
-        describe('when the initial holder has enough balance', function () {
-          const amount = initialSupply;
-
-          it('transfers the requested amount', async function () {
-            await this.token.transferFrom(initialHolder, to, amount, { from: spender });
-
-            (await this.token.balanceOf(initialHolder)).should.be.bignumber.equal('0');
-
-            (await this.token.balanceOf(to)).should.be.bignumber.equal(amount);
-          });
-
-          it('decreases the spender allowance', async function () {
-            await this.token.transferFrom(initialHolder, to, amount, { from: spender });
-
-            (await this.token.allowance(initialHolder, spender)).should.be.bignumber.equal('0');
-          });
-
-          it('emits a transfer event', async function () {
-            const { logs } = await this.token.transferFrom(initialHolder, to, amount, { from: spender });
-
-            expectEvent.inLogs(logs, 'Transfer', {
-              from: initialHolder,
-              to: to,
-              value: amount,
-            });
-          });
-
-          it('emits an approval event', async function () {
-            const { logs } = await this.token.transferFrom(initialHolder, to, amount, { from: spender });
-
-            expectEvent.inLogs(logs, 'Approval', {
-              owner: initialHolder,
-              spender: spender,
-              value: await this.token.allowance(initialHolder, spender),
-            });
-          });
-        });
-
-        describe('when the initial holder does not have enough balance', function () {
-          const amount = initialSupply.addn(1);
-
-          it('reverts', async function () {
-            await shouldFail.reverting.withMessage(this.token.transferFrom(
-              initialHolder, to, amount, { from: spender }), 'SafeMath: subtraction overflow'
-            );
-          });
-        });
-      });
-
-      describe('when the spender does not have enough approved balance', function () {
-        beforeEach(async function () {
-          await this.token.approve(spender, initialSupply.subn(1), { from: initialHolder });
-        });
-
-        describe('when the initial holder has enough balance', function () {
-          const amount = initialSupply;
-
-          it('reverts', async function () {
-            await shouldFail.reverting.withMessage(this.token.transferFrom(
-              initialHolder, to, amount, { from: spender }), 'SafeMath: subtraction overflow'
-            );
-          });
-        });
-
-        describe('when the initial holder does not have enough balance', function () {
-          const amount = initialSupply.addn(1);
-
-          it('reverts', async function () {
-            await shouldFail.reverting.withMessage(this.token.transferFrom(
-              initialHolder, to, amount, { from: spender }), 'SafeMath: subtraction overflow'
-            );
-          });
-        });
-      });
-    });
-
-    describe('when the recipient is the zero address', function () {
-      const amount = initialSupply;
-      const to = ZERO_ADDRESS;
-
-      beforeEach(async function () {
-        await this.token.approve(spender, amount, { from: initialHolder });
-      });
-
-      it('reverts', async function () {
-        await shouldFail.reverting.withMessage(this.token.transferFrom(
-          initialHolder, to, amount, { from: spender }), 'ERC20: transfer to the zero address'
-        );
-      });
-    });
-  });
+  shouldBehaveLikeERC20('ERC20', initialSupply, initialHolder, recipient, anotherAccount);
 
   describe('decrease allowance', function () {
     describe('when the spender is not the zero address', function () {
@@ -493,14 +330,8 @@ contract('ERC20', function ([_, initialHolder, recipient, anotherAccount]) {
     });
   });
 
-  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) {
+    shouldBehaveLikeERC20Approve('ERC20', initialHolder, recipient, initialSupply, function (owner, spender, amount) {
       return this.token.approveInternal(owner, spender, amount);
     });
 
@@ -512,84 +343,4 @@ contract('ERC20', function ([_, initialHolder, recipient, anotherAccount]) {
       });
     });
   });
-
-  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.withMessage(approve.call(this, owner, ZERO_ADDRESS, supply),
-          'ERC20: approve to the zero address'
-        );
-      });
-    });
-  }
 });