Mock Objects in Unit Tests (8 tags)
Unit testing your code against a service or process that's either too expensive (commercial databases) or just not done yet is something you can deal with by simulating the other piece with a mock object. EasyMock can suffice in some cases, but it can only create mock objects for interfaces. Mocquer, based on the Dunamis project, can create mocks for classes, too. Lu Jian shows how it works.
Towards Bug-Free Code (2 tags)
Test-driven development sometimes sounds better than it turns out to be. Early decisions to tightly couple functional parts of your system can make it a lot less amenable to testing than it ought to be. As Ashwin Jayaprakash shows, J2SE 5.0's generics make working with abstract classes and interfaces easier than it used to be, which encourages loose coupling and facilitates testing.
Unit Test Your Struts Application (2 tags)
Consistent unit testing is an essential part of development, but web applications aren't necessarily well-suited to unit testing--how to you validate the "correctness" of a returned stream of text or HTML? Lu Jian has an answer in the form of StrutsUT, a Cactus-based library for unit testing Struts web apps.