jcoverage/gpl is a free code-coverage tool for Java™ programmers that allows them to measure the effectiveness of their Java tests and how much of a software programs code has been tested.
jcoverage/gpl identifies how many times each line of code in your application has been executed and you can see which parts of your software remain untested. After instrumenting your code and running your tests, a report is generated allowing you to view information coverage figures from a project level right down to the individual line of code. This process is called code coverage.
jcoverage works by modifying your Java™ classes at the bytecode level. It also works against code that you do not have the source code for, as well as code that has itself been modified at byte-code level, for example, JDO data classes and aspect-derived code - something no other industry tool offers.