jMock
Link - http://www.jmock.org/
JMock is a library that supports test-driven development1 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.