added a test helper with common constants (#1400)

* signing prefix added

* Minor improvement

* Tests changed

* Successfully tested

* Minor improvements

* Minor improvements

* Revert "Dangling commas are now required. (#1359)"

This reverts commit a6889776f4.

* updates

* fixes #1206

(cherry picked from commit 58a42443df)

test/token/ERC20/TokenVesting.test.js

@@ -3,6 +3,7 @@ const { EVMRevert } = require('../../helpers/EVMRevert');
 const { latestTime } = require('../../helpers/latestTime');
 const { increaseTimeTo, duration } = require('../../helpers/increaseTime');
 const { ethGetBlock } = require('../../helpers/web3');
+const { ZERO_ADDRESS } = require('../../helpers/constants');
 
 const BigNumber = web3.BigNumber;
 
@@ -15,7 +16,6 @@ const TokenVesting = artifacts.require('TokenVesting');
 
 contract('TokenVesting', function ([_, owner, beneficiary]) {
   const amount = new BigNumber(1000);
-  const ZERO_ADDRESS = '0x0000000000000000000000000000000000000000';
 
   beforeEach(async function () {
     this.start = (await latestTime()) + duration.minutes(1); // +1 minute so it starts after contract instantiation