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/access/Roles.test.js

@@ -1,13 +1,11 @@
 const { assertRevert } = require('../helpers/assertRevert');
-
+const { ZERO_ADDRESS } = require('../helpers/constants');
 const RolesMock = artifacts.require('RolesMock');
 
 require('chai')
   .should();
 
 contract('Roles', function ([_, authorized, otherAuthorized, anyone]) {
-  const ZERO_ADDRESS = '0x0000000000000000000000000000000000000000';
-
   beforeEach(async function () {
     this.roles = await RolesMock.new();
   });