Forwards compatible: you can run your old test suites in JUnit 4
Backwards compatible: your old test runners can run the new test suites
To enable your JUnit 4 tests to run in JUnit 3 environments, wrap them in a JUnit4TestAdapter
Add this method to your JUnit 4 test class:
public static junit.framework.Test suite() {
return new JUnit4TestAdapter(TestClassName.class);
}