Code coverage allows you to see how much of your code is being executed during unit tests, so you can understand how effective these tests are.
The following code coverage runners are available in IntelliJ IDEA:
IntelliJ IDEA code coverage runner (recommended).
EMMA open-source toolkit. Note that EMMA is not supported by the author any more, and works with Java 7 only when frame validation turned off (pass
-noverifyto the process).