Mockito
Most popular Mocking framework for unit tests written in Java
...Mockito 3.x requires Java 8, but otherwise doesn’t introduce any breaking changes compared to the 2.x series. Mockito 2.25.0 had an important feature added for anyone using mockito-inline. In particular anyone using Kotlin (which demands using mockito-inline) and PowerMock (which exacerbates the problem even more) will want to add this to all of their test classes to avoid a large memory leak. Fancy getting world-wide visibility and building up an eternal fame of an OSS contributor? Use the latest version! Hack and experiment. Speak up at the mailing list. ...