JUnit: “A programmer-friendly testing framework for Java”. Used by the Spring Framework in its test suite and supported in the Spring TestContext Framework.

TestNG: A testing framework inspired by JUnit with added support for test groups, data-driven testing, distributed testing, and other features. Supported in the Spring TestContext Framework

AssertJ: “Fluent assertions for Java”, including support for Java 8 lambdas, streams, and other features.

Mock Objects: Article in Wikipedia.

MockObjects.com: Web site dedicated to mock objects, a technique for improving the design of code within test-driven development.

Mockito: Java mock library based on the Test Spy pattern. Used by the Spring Framework in its test suite.

EasyMock: Java library “that provides Mock Objects for interfaces (and objects through the class extension) by generating them on the fly using Java’s proxy mechanism.”

JMock: Library that supports test-driven development of Java code with mock objects.

DbUnit: JUnit extension (also usable with Ant and Maven) that is targeted at database-driven projects and, among other things, puts your database into a known state between test runs.

The Grinder: Java load testing framework.

SpringMockK: Support for Spring Boot integration tests written in Kotlin using MockK instead of Mockito.