JayWalker is an open-source software analysis tool which can be used either at build or deployment time to interrogate a Java application's compiled artifacts and generates static and interactive graphical reports from it. In turn, a software professional can interpret and use these reports to improve software quality and to understand the current state of the software application in question.

Multi-threaded/Multi-JVM System Testing Extension for JUnit.

jMock 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. The jMock package: 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. is easy to extend.

Sonar is an enterprise quality control tool, distributed under the terms of the GNU LGPL. Its basic purpose is to join existing continuous integration tools to place Java development projects under quality control.