testing : Java Glossary

1. Unit testing: or white box testing. You write little routines to exhaustively test each execution branch of your method. I often refer to such a suite as a test harness. You test each method in isolation. Unit tests are best at finding implementation errors, such as off-by-one loops. Tools such as JUNIT can help you compose these tests.
2. Black-box testing: or system level testing. This is best at finding integration errors. The tester deliberately does not look at how a function is implemented. He is out to catch miscommunications between programmers on how to use each others’ classes. The tester avoids looking at the code to avoid falling into the same traps and presumptions the programmers did.

For more complex classes, you use a tool like JUnit.