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

test/helpers/constants.js

@@ -0,0 +1,6 @@
+const BigNumber = web3.BigNumber;
+
+module.exports = {
+  ZERO_ADDRESS: '0x0000000000000000000000000000000000000000',
+  MAX_UINT256: new BigNumber(2).pow(256).minus(1),
+};