J.B. Rainsberger talked about how contract tests can be used to test the interaction between classes when using a mockist approach to developer testing. He wondered aloud if it would be possible to write these kinds of tests using abstract classes and JUnit 4. The answer is yes, with some caveats, as Ben Rady demonstrates it. You can watch this presentation called "Contract Tests in JUnit 4" on the directory of Java videos and tutorials.
