reapply "Proposal for balance redesign (#13)"

* intial implementation

* small refactoring

* changed readme

* implemente pr comments

* fixed linter errors

* addressed remaning comments

* fixed integration test

* removed array usage

* using balanceCurrent for fetching tracker balance

* fixed small issue in test

Author: JGcarv

README.md

@@ -49,16 +49,36 @@ All returned numbers are of type [BN](https://github.com/indutny/bn.js).
 ---
 
 ### balance
-#### async balance.current (account)
-Returns the current Ether balance of an account.
+Helper to keep track of ether balances of a specific account
 
-#### async balance.difference (account, promiseFunc)
-Returns the change in the Ether balance of an account caused by executing `promiseFunc` (which will be awaited on).
+#### balance current
+##### async balance.current(account)
+Returns the current balance of an account
+```javascript
+const balance = await balance.current(account)
+```
 
+#### balance tracker
+##### async balance.get
+Returns the current Ether balance of an account.
+```javascript
+const balanceTracker = await balance.tracker(account) //instantiation
+const accounBalance = await balanceTracker.get() //returns the current balance of account
+```
+##### async balance.delta
+Returns the change in the Ether since the last check(either `get()` or `delta()`)
+
+```javascript
+const balanceTracker = await balance.tracker(receiver)
+send.ether(sender, receiver, ether('10'))
+(await balanceTracker.delta()).should.be.bignumber.equal('10');
+(await balanceTracker.delta()).should.be.bignumber.equal('0');
+```
+Or using `get()`:
 ```javascript
-(await balance.difference(receiver, () =>
-  send.ether(sender, receiver, ether('1')))
-).should.be.bignumber.equal(ether('1'));
+const balanceTracker = await balance.tracker(account) //instantiation
+const accounBalance = await balanceTracker.get() //returns the current balance of account
+(await balanceTracker.delta()).should.be.bignumber.equal('0');
 ```
 
 ---

src/balance.js

@@ -1,17 +1,32 @@
 const { BN } = require('./setup');
 
-async function balanceCurrent (account) {
-  return new BN(await web3.eth.getBalance(account));
+class Tracker {
+  constructor (acc) {
+    this.account = acc;
+  }
+  async delta () {
+    const current = await balanceCurrent(this.account);
+    const delta = current.sub(this.prev);
+    this.prev = current;
+    return delta;
+  }
+  async get () {
+    this.prev = await balanceCurrent(this.account);
+    return this.prev;
+  }
+}
+
+async function balanceTracker (owner) {
+  const tracker = new Tracker(owner);
+  await tracker.get();
+  return tracker;
 }
 
-async function balanceDifference (account, promiseFunc) {
-  const balanceBefore = new BN(await web3.eth.getBalance(account));
-  await promiseFunc();
-  const balanceAfter = new BN(await web3.eth.getBalance(account));
-  return balanceAfter.sub(balanceBefore);
+async function balanceCurrent (account) {
+  return new BN(await web3.eth.getBalance(account));
 }
 
 module.exports = {
   current: balanceCurrent,
-  difference: balanceDifference,
+  tracker: balanceTracker,
 };

test-integration/simple-project-truffle-5.x/test/accounts.test.js

@@ -3,9 +3,8 @@ const { balance, BN, ether, send } = require('openzeppelin-test-helpers');
 contract('accounts', function (accounts) {
   it('sends ether and tracks balances', async function () {
     const value = ether('42', 'ether');
-
-    (await balance.difference(accounts[0], () =>
-      send.ether(accounts[0], accounts[1], value)
-    )).should.be.bignumber.equals(value.neg());
+    const tracker = await balance.tracker(accounts[0]);
+    await send.ether(accounts[0], accounts[1], value);
+    (await tracker.delta()).should.be.bignumber.equals(value.neg());
   });
 });

test/src/balance.test.js

@@ -11,17 +11,44 @@ contract('balance', function ([sender, receiver]) {
     });
   });
 
-  describe('difference', function () {
+  describe('balance tracker', function () {
+    it('returns current balance ', async function () {
+      const tracker = await balance.tracker(receiver);
+      (await tracker.get()).should.be.bignumber.equal(await web3.eth.getBalance(receiver));
+    });
+
+    it('get() adds a new checkpoint ', async function () {
+      const tracker = await balance.tracker(sender);
+      await send.ether(sender, receiver, ether('1'));
+      await tracker.get();
+      (await tracker.delta()).should.be.bignumber.equal('0');
+    });
+
+    it('returns correct deltas after get() checkpoint', async function () {
+      const tracker = await balance.tracker(receiver);
+      await send.ether(sender, receiver, ether('1'));
+      await tracker.get();
+      await send.ether(sender, receiver, ether('1'));
+      (await tracker.delta()).should.be.bignumber.equal(ether('1'));
+    });
+
     it('returns balance increments', async function () {
-      (await balance.difference(receiver, () =>
-        send.ether(sender, receiver, ether('1')))
-      ).should.be.bignumber.equal(ether('1'));
+      const tracker = await balance.tracker(receiver);
+      await send.ether(sender, receiver, ether('1'));
+      (await tracker.delta()).should.be.bignumber.equal(ether('1'));
     });
 
     it('returns balance decrements', async function () {
-      (await balance.difference(sender, () =>
-        send.ether(sender, receiver, ether('1')))
-      ).should.be.bignumber.equal(ether('-1'));
+      const tracker = await balance.tracker(sender);
+      await send.ether(sender, receiver, ether('1'));
+      (await tracker.delta()).should.be.bignumber.equal(ether('-1'));
+    });
+
+    it('returns consecutive deltas', async function () {
+      const tracker = await balance.tracker(sender);
+      await send.ether(sender, receiver, ether('1'));
+      await tracker.delta();
+      (await tracker.delta()).should.be.bignumber.equal('0');
     });
   });
 });