Creating mock objects for Test Driven Development

EasyMock - EasyMock provides Mock Objects for interfaces (and objects through the class extension) 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.

http://easymock.org/index.html
http://easymock.org/EasyMock3_0_Documentation.html

Mockito - Mockito library enables mocks creation, verification and stubbing.

http://mockito.org/
http://docs.mockito.googlecode.com/hg/org/mockito/Mockito.html

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

http://www.jmock.org/
http://www.jmock.org/cheat-sheet.html
http://www.jmock.org/cookbook.html