Can't test my code, flow goes into JUnit library Follow

Hi,

I am writing a Java class library, with some JUnit tests.

The tests are written, fully annotated, etc, but when I run a test, it steps into the class definitions for JUnit and says at the top, source not available. It doesn't go into my code under test (I am using debug test), so I  can't see the code get tested. See the attached picture.

Please help. Any ideas much appreciated!

Thanks