jMock is a library that supports test-driven development of Java code with mock objects.

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.