Adding some additional tests

test/StandardToken.js

 'use strict';
 
 const assertJump = require('./helpers/assertJump');
+const expectThrow = require('./helpers/expectThrow');
 var StandardTokenMock = artifacts.require('./helpers/StandardTokenMock.sol');
 
 contract('StandardToken', function(accounts) {
@@ -70,6 +71,17 @@ contract('StandardToken', function(accounts) {
     }
   });
 
+  it('should throw an error when trying to transferFrom more than _from has', async function() {
+    let balance0 = await token.balanceOf(accounts[0]);
+    await token.approve(accounts[1], 99);
+    try {
+      await token.transferFrom(accounts[0], accounts[2], balance0+1, {from: accounts[1]});
+      assert.fail('should have thrown before');
+    } catch (error) {
+      assertJump(error);
+    }
+  });
+
   describe('validating allowance updates to spender', function() {
     let preApproved;
 
@@ -88,6 +100,13 @@ contract('StandardToken', function(accounts) {
     })
   });
 
+  it('should increase by 50 then set to 0 when decreasing by more than 50', async function() {
+    await token.approve(accounts[1], 50);
+    await token.decreaseApproval(accounts[1], 60);
+    let postDecrease = await token.allowance(accounts[0], accounts[1]);
+    postDecrease.should.be.bignumber.equal(0);
+});
+
   it('should throw an error when trying to transfer to 0x0', async function() {
     let token = await StandardTokenMock.new(accounts[0], 100);
     try {