JMockit

JMockit is a useful set of utilities that will help you perform test written using frameworks like JUnit or TestNG. The tools rely on the Java 5 SE instrumentation feature (the java.lang.instrument package), internally using the ASM library to modify bytecode at runtime.

There are currently six different components/tools in the JMockit toolkit, which can be used individually, as follows:

JMockit Core - a single class with a small set of static methods, which allow arbitrary methods and constructors of any other class to be replaced with mock implementations at runtime.

JMockit Annotations - provides a pair of Java 5 language annotations for that purpose. Constraints on the number of expected invocations for each mock can be provided.

JMockit Expectations - provide a record/replay model for writing tests, which allows for more succinct tests.

JMockit Hibernate Emulation - a fake implementation of the Hibernate 3 Core APIs, which can be installed in place of the real implementation with a simple JVM initialization argument. When those tests run with the emulation in effect, they won't use the O/R mapping information, nor will they access any real database. All persistence operations, including HQL queries, will be executed against the equivalent of an in-memory database.

JMockit AOP - supports the application of advice to any method or constructor. The usual types of advice are supported: before, after, and around.