Stubs vs. Mocks

            Having started to learn about stubs with relation to testing in class, I went to do some further research on the functionality and usefulness of this testing strategy. I found a great deal of articles comparing stubs with mocks and evaluating their differences. I haven’t heard of mock testing before, so this was interesting to look into. Turns out, it’s pretty similar to some work we did in class. I found this great article detailing the differences which also gives a simple, understandable example.

            The main difference in stubs vs mocks is that stubs are looking to see a certain behavior, while mocks are also setting an expectation and then verifying that expectation. This is demonstrated with the use of a couple examples. Stub methods are created in the example by not doing anything but printing out “_____ is working fine.” This is to check that the correct method is being called and in the proper context. On the other hand, a mock uses a third party library (Mockito) which creates a mock Mathematics object in a test setup. Then, still in setup, the expectation is set: when(maths.sub(2,1).thenReturn(1); This is just saying 2 – 1 = 1. And finally, this expectation is verified in the test with Assert.assertEquals(1, s.subNumbers(2,1)); If this explanation seems choppy, sorry, I tried to condense 44 lines of code down to just this. Anyways, the idea is that a mock object is made, expectations are set, and then they’re verified. So both stubs and mocks are useful kind of white-box-ish testing styles, but mocks seem to have a higher level of testability. This doesn’t mean they’re necessarily better or more useful, but they have their purpose too.