jMock 2 is a library for testing Java code using mock objects.

See:
Description

jMock 2

org.jmock	The jMock "Domain-Specific Embedded Language" API.
org.jmock.api	The stable API that is used to extend jMock at it's published plug-in points.
org.jmock.auto
org.jmock.integration.junit3	Integrates jMock with JUnit 3.
org.jmock.integration.junit4	Integrates jMock with JUnit 4.
org.jmock.lib	Implementations of the core interfaces that are used to adjust or extend jMock's basic functionality.
org.jmock.lib.action	Actions that fake the behaviour of mocked invocations.
org.jmock.lib.concurrent	Classes to help test concurrent code with jMock.
org.jmock.lib.legacy	Plugins that make it easier to use jMock with legacy code.
org.jmock.lib.script	Plugins that make it easier to write custom actions by scripting their behaviour with BeanShell.
org.jmock.syntax	Interfaces that define jMock's Domain Specific Embedded Language.

jMock 2 is a library for testing Java code using mock objects. Mock objects help you design and test the interactions between the objects in your programs.

jMock 2:

• 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.
• acts as a "domain-specific embedded language" for specifying expectations so it is easy to read and understand the intent of tests with mock objects.
• uses real method calls to specify expectations, so code can be easily refactored in modern IDEs.
• is easy to extend.

More information can be found on the jMock website (www.jmock.org).