Today I lost a bit of time trying to make Eclipse 3.5 run JUnit 4 test cases. It complained about "no tests found". I discovered that JUnit 4 was not on the build path, and I couldn't add it because while Eclipse had an entry in its Build Path -> Libraries -> Add Libraray -> JUnit -> JUnit 4, it just said "Not Found" and that was it. Adding it as an external JAR helped with the compiling but didn't enable the test runners either.

It turned out that this was actually a packaging bug in the Eclipse packages in Fedora 12 and that you have to also install the eclipse-pde package.
I found the solution on this thread in the Fedora forums