convert SimpleToken to initializers

contracts/examples/SimpleToken.sol

 pragma solidity ^0.4.24;
 
 
+import "../Initializable.sol";
 import "../token/ERC20/ERC20.sol";
 
 
@@ -10,7 +11,7 @@ import "../token/ERC20/ERC20.sol";
  * Note they can later distribute these tokens as they wish using `transfer` and other
  * `ERC20` functions.
  */
-contract SimpleToken is ERC20 {
+contract SimpleToken is Initializable, ERC20 {
 
   string public constant name = "SimpleToken";
   string public constant symbol = "SIM";
@@ -21,7 +22,7 @@ contract SimpleToken is ERC20 {
   /**
    * @dev Constructor that gives msg.sender all of existing tokens.
    */
-  constructor() public {
+  function initialize() public initializer {
     _mint(msg.sender, INITIAL_SUPPLY);
   }
 

contracts/mocks/SimpleTokenMock.sol

+pragma solidity ^0.4.24;
+
+import "../Initializable.sol";
+import "../examples/SimpleToken.sol";
+
+contract SimpleTokenMock is Initializable, SimpleToken {
+  constructor() public {
+    SimpleToken.initialize();
+  }
+}

test/examples/SimpleToken.test.js

 const { decodeLogs } = require('../helpers/decodeLogs');
-const SimpleToken = artifacts.require('SimpleToken');
+const SimpleToken = artifacts.require('SimpleTokenMock');
 
 const BigNumber = web3.BigNumber;