Class Not Found Exception when running JUnit test

This appears to occur because only the source code is compiling when you use mvn clean compile (I'm using maven 3.1.0 so I'm not sure if it always behaved like this).

If you run mvn test, the test code will compile as well, but then it runs the tests (which may not be immediately desirable if you're trying to run them through Eclipse.) The way around this is to add test-compile to your Maven command sequence whenever you do a mvn clean. For example, you would run mvn clean compile test-compile.

I had a similar problem with my tests and found somewhere in the Web, that you have to go to Build Path in your project's properties and move Maven Dependencies above JRE System Library. That seems to have worked for me.