docs(mocks): add recipe for creating mocks with DI

[jeffbcross]

I added a recipe for mocking classes with DI. Maybe I'm doing it wrong, so please give a good review before merging :).

[vojtajina]

Can you write it using https://github.com/angular/di.js/blob/master/example/testing/coffee.spec.js ?

[vojtajina]

btw, HttpBackend should ask for XMLHttpRequest, not Window.

[jeffbcross]

@vojtajina Can you give some guidance on how to inject a constructor like XMLHttpRequest without attaching it to another object?

[vojtajina]

function HttpRequest() {
  return window.XMLHttpRequest;
}

class HttpBackend {
  @Inject(HttpRequest)
  constructor(HttpRequest) {
    // ...
  }
}

We need a cleaner way for this. See #21 and #22

[tusharmath]

I don't think creating mocks manually, is a scalable solution. Every time there is an update in the original class you might have to update your mocks also. I would rather prefer using Stubs. Use a library like - Sinon to stub your requests that are dependent on the XMLHttpRequest object. Any thoughts, where I could be wrong?

[caitp]

@tusharmath sinon actually provides quite a few mocks itself... mocks and stubs sort of solve different problems. Mocking a class which performs async ops is attractive for testing because it lets your tests have a bit more control, and the ability to run synchronously. Stubs are useful for letting you perform assertions at a certain point, or asserting that the particular subroutine was invoked the way you expect it to be.

Both are great for testing, but they don't solve the same problems

[tusharmath]

@caitp After seeing a lil bit here and there I finally got your point. Thanks!

[tusharmath]

Why is one supposed to pass HttpBackend to the Injector ctor?

[tusharmath]

Where would modules like - Mockery fit in? Are both of them solving the same problem?