JMock is a library that supports test-driven development1 of Java2 code with mock objects3.

Mock objects help you design and test the interactions between the objects in your programs.

The jMock library:

* makes it quick and easy to define mock objects, so you don't break the rhythm of programming.
* lets you precisely specify the interactions between your objects, reducing the brittleness of your tests.
* works well with the autocompletion and refactoring features of your IDE
* plugs into your favourite test framework
* is easy to extend.