jMock is a library for testing Java code using mock objects1. Mock objects help you design and test the interactions between the objects in your programs. The jMock package: * makes it quick and easy to define mock objects, so you don't break the rhythm of programming. * lets you define flexible constraints over object interactions, reducing the brittleness of your tests. * is easy to extend.

EasyMock provides Mock Objects for interfaces in JUnit tests by generating them on the fly using Java's proxy mechanism. Due to EasyMock's unique style of recording expectations, most refactorings will not affect the Mock Objects. So EasyMock is a perfect fit for Test-Driven Development.