Java Power Tools

Chapter 12. Maximizing Test Coverage with Cobertura

Test Coverage

Unit testing is recognized as a crucial part of modern software development practices. Nevertheless, for a number of reasons discussed at length elsewhere, it is often done insufficiently and poorly. Basically, there are two main things that can make a unit test ineffective: it can execute the code but test the business logic poorly or not at all, or it can neglect to test parts of the code. The first case is fairly hard to detect automatically. In this chapter we will look at the second type of issue, which is the domain of test coverage tools.

It is fairly clear that if a part of your code isn’t being executed during the unit tests, then it isn’t being tested. And this is often a Bad Thing. This is where test coverage tools come it. Test coverage tools observe your code during unit tests, recording which lines have been executed (and therefore subject to at least some testing). And although the fact that a line of code is executed during unit tests offers absolutely no guarantee that it executes correctly (it is easy enough to write unit tests that exercise an entire class without testing any business logic at all!), in practice it is always preferable to minimize the amount of code that is not tested at all.

Cobertura^[10] is a free, open source test coverage tool for Java. Cobertura works by instrumenting the compiled bytecode from your application, inserting code to detect and log which lines have and have not ...