Android Studio无法解析org.junit

I am using JUnit tests in Android Studio 1.2.2. The tests run without a problem. The only thing that puzzles me is that Android Studio cannot resolve the actual org.junit package. Obviously it does resolve it otherwise the tests wouldn't run. But the import and annotations are marked red in Android Studio as shown here. Is this a bug in Android Studio? I tried rebuilding the app and restarting Android Studio but this doesn't correct the problem.I am using JUnit tests in Android Studio 1.2.2.