Intellij IDEA doesn't detect changes
VCS -> Refresh File Status solved this for me, when Intellij suddenly stopped noticing changes.
SOLUTION:
Error magically gone after 2 things:
I imported this project into eclipse and run JUNit test from eclipse. Then I returned to IDEA and deleted all Eclipse specific files.
I synchronized my project (File->Synchronize).
I don't know what actually was the solution of problem, but for suggestions I accept @SeanLandsman's answer
Answer to an old question, but:
If you're using a Run Configuration, make sure in the "Before Launch" section of the "Run/Debug Configurations" dialog, you have added "Build". It seems to get removed from this dialog sometimes, even if you have it added in the default settings.