balanceDifference tests and application (#1514)

* Added balanceDifference tests.

* Added balanceDifference tests.

* Now using balanceDifference in all (most) tests.

* Fixed typo.

test/helpers/balanceDifference.js

@@ -1,6 +1,6 @@
-async function balanceDifference (account, promise) {
+async function balanceDifference (account, promiseFunc) {
   const balanceBefore = web3.eth.getBalance(account);
-  await promise();
+  await promiseFunc();
   const balanceAfter = web3.eth.getBalance(account);
   return balanceAfter.minus(balanceBefore);
 }

test/helpers/test/balanceDifference.test.js

@@ -0,0 +1,22 @@
+const { balanceDifference } = require('../balanceDifference');
+const { sendEther } = require('../sendTransaction');
+const { ether } = require('../ether');
+
+const BigNumber = web3.BigNumber;
+require('chai')
+  .use(require('chai-bignumber')(BigNumber))
+  .should();
+
+contract('balanceDifference', function ([sender, receiver]) {
+  it('returns balance increments', async function () {
+    (await balanceDifference(receiver, () =>
+      sendEther(sender, receiver, ether(1)))
+    ).should.be.bignumber.equal(ether(1));
+  });
+
+  it('returns balance decrements', async function () {
+    (await balanceDifference(sender, () =>
+      sendEther(sender, receiver, ether(1)))
+    ).should.be.bignumber.equal(ether(-1));
+  });
+});