Robert Rees was astute enough to point out that it can be difficult to combine the expected-exception feature of JUnit 4 with Theories.  What if we want to say that any Comparable in our system should throw a null pointer exception if compared with null?  (By the way, it appears this is neither required nor disallowed by the Comparable contract.)

The current answer is a bit ugly: you need to combine the @Test and @Theory annotations:

@Theory @Test(expected=NullPointerException.class)
public void compareToNullThrowsNpe(Comparable c) {
   c.compareTo(null);
}