Mockito

Mockito is an Open Source Java Mocking and Unit Testing Tool. Mockito is a popular open source Java mocking framework. It helps developers to write clean, well-designed and loosely-coupled code.

Features:
     1. It can be used to write Behaviour Driven Development style tests with syntactic sugar facilitates
     2. It offers nice, easily readable syntax. It also provides some annotations needed for reducing boilerplate code
     3. Mockito allows writing of relaxed tests

More Information and Official Website:
Download : http://site.mockito.org/