Code coverage in IntelliJ IDEA allows you to see the extent to which your code has been executed. It also lets you verify the extent to which your code is covered by unit tests, so that you can estimate how effective these tests are.
The following code coverage runners are available in IntelliJ IDEA:
IntelliJ IDEA code coverage runner (recommended)
EMMA is an open-source toolkit. Note that EMMA is not supported by the author any more, and works with Java 7 only when frame validation is turned off (pass
-noverifyto the process).