Mockito is an open source testing framework for Java. The framework allows the creation of Test Double objects called, “Mock Objects” in automated unit tests for the purpose of Test-driven Development (TDD) or Behavior Driven Development (BDD).
Mockito compared to EasyMock seems to be more easily and has more flexibility. First it’s able to mock up interfaces as well as classes. You doesn’t need additional Jar libraries. Furthermore there isn’t any replay mode. First you have to stub and afterwards you have to verificate your mocked classes or interfaces. Further advantages could be read here