Alex Rivera | Logout

What is the difference between integration and unit tests?

Asked 2008-08-14T06:27:57.207
361

I know the so-called textbook definition of unit tests and integration tests. What I am curious about is when it is time to write unit tests... I will write them to cover as many sets of classes as possible.

For example, if I have a Word class, I will write some unit tests for the Word class. Then, I begin writing my Sentence class, and when it needs to interact with the Word class, I will often write my unit tests such that they test both Sentence and Word... at least in the places where they interact.

Have these tests essentially become integration tests because they now test the integration of these 2 classes, or is it just a unit test that spans 2 classes?

In general, because of this uncertain line, I will rarely actually write integration tests... or is my using the finished product to see if all the pieces work properly the actual integration tests, even though they are manual and rarely repeated beyond the scope of each individual feature?

Am I misunderstanding integration tests, or is there really just very little difference between integration and unit tests?

unit-testing integration-testing
Edit
Report

1 Answer

65

When I write unit tests I limit the scope of the code being tested to the class I am currently writing by mocking dependencies. If I am writing a Sentence class, and Sentence has a dependency on Word, I will use a mock Word. By mocking Word I can focus only on its interface and test the various behaviors of my Sentence class as it interacts with Word's interface. This way I am only testing the behavior and implementation of Sentence and not at the same time testing the implementation of Word.

Once I've written the unit tests to ensure Sentence behaves correctly when it interacts with Word based on Word's interface, then I write the integration test to make sure that my assumptions about the interactions were correct. For this I supply the actual objects and write a test that exercises a feature that will end up using both Sentence and Word.

answered 2008-09-01T19:33:42.823

Your Answer