Run JUnit test programmatically loading different .class files

i'm currently able to run a JUnit test programmatically doing something like this:

JUnitCore junit = new JUnitCore();
Result result = new Result();

File root = new File("rootWhereSommatoreTest.classIS");
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[]{root.toURI().toURL() });
Class<?> cls = classLoader.loadClass("SommatoreTest");  
result = junit.run(cls);
return result;

What i dislike about this code is that SommatoreTest.class must be in the same directory as Sommatore.class to work. So i was wondering if it was possible to run a Junit test, loading separately .class files from different directories in the same ClassLoader, enabling SommatoreTest to "see" Sommatore.

Thanks in advance for your answer! And keep up the good work!