Bug 1070845 - [sharedtest] unit test refactoring for new version chai.assert api (rebased)

test_agent used very old version chai library version=0.5.3 in the current version=1.9.1 deepEqua
nit: it's easier to write it like this:
```js
ImageUtils.resizeAndCropToCover(self.inputBlob, W / 2, H / 2)
  .then(() => sinon.assert.notCalled(spy)).then(done, done);
```