For some time I've been bugged by a Netbeans problem that I couldn't find any solution to. When running a unit test from within Netbeans from time to time it happended that the tests just failed. They seemed to be executed in an old state. Running them again didn't help either, it seemed that some parts of the project didn't get recompiled. When executing the tests from a command line Maven build there were never any problems and afterwards the tests could be run again from Netbeans. The problem only occured very infrequently but nevertheless it was really annoying. I started not running the tests from Netbeans at all but only using Maven. That is also not a good solution as you either run all tests or have to edit the command line all the time for running only a single test.
Recently I noticed what caused the problem: Netbeans has its compile on save feature on for tests. This means it is using its internal incremental compile feature which doesn't seem to work fine at least for some project setups.
You can disable it in the project properties on the Build/Compile node. I haven't seen any problems since disabling it. Saves me a lot of time to run the tests from the IDE again.