Mutant Jesters
There are many tools that can increase your visibility of unit-tests - coverage tools such as Clover can show you uncovered parts of your code or execution paths that are never followed. This makes it very easy to expand your test coverage.
But that's not all...
Jester is a code mutation tool by Ivan Moore that can show you much more than this - how effective your tests are rather than just how well covered your code is. An automated test tester.
One of the rules of test driven development is that any line of code in your system that isn't there to make a test pass is redundant - get rid of it! Jester helps you enforce this by mutating your code. It's pretty simple - if it can change a line of source code, rerun the tests and they still pass, it's redundant code. This is reflected in a nice little HTML report.
It's easy to write a test that executes an entire chunk of code and pleases a coverage tool - however there's no point if it isn't actually testing all the results and interactions. Read Ivan's paper for a more in depth discussion on the topic. This can be used to either find out your testing weaknesses or identify useless code.
So, once you think your code has pretty good test coverage, try testing how effective your tests actually are. It's very eye-opening.
Jester should be in the core distribution of Maven, methinks :)
[Joe's Jelly]
So totally cool.
