Why do we need mocking frameworks?

Question

I have worked with code which had NUnit test written. But, I have never worked with mocking frameworks. What are they? I understand dependency injection and how it helps to improve the testability. I mean all dependencies can be mocked while unit testing. But, then why do we need mocking frameworks? Can't we simply create mock objects and provide dependencies. Am I missing something here? Thanks.

Answer 1

• It makes mocking easier
• They usually allow you to express testable assertions that refer to the interaction between objects.

Here you have an example:

var extension = MockRepository
    .GenerateMock<IContextExtension<StandardContext>>();
  var ctx = new StandardContext();
  ctx.AddExtension(extension);
  extension.AssertWasCalled(
    e=>e.Attach(null), 
    o=>o.Constraints(Is.Equal(ctx)));

You can see that I explicitly test that the Attach method of the IContextExtension was called and that the input parameter was said context object. It would make my test fail if that did not happen.

Answer 2

You can create mock objects by hand and use them during testing using Dependency Injection frameworks...but letting a mocking framework generate your mock objects for you saves time.

As always, if using the framework adds too much complexity to be useful then don't use it.

Answer 3

Sometimes when working with third-party libraries, or even working with some aspects of the .NET framework, it is extremely difficult to write tests for some situations - for example, an HttpContext, or a Sharepoint object. Creating mock objects for those can become very cumbersome, so mocking frameworks take care of the basics so we can spend our time focusing on what makes our applications unique.