Mark unit test as an expected failure in JUnit

I’m not quite getting the specifics of your scenario, but here’s how I generally test for expected failure:

The slick new way:

@Test(expected=NullPointerException.class)
public void expectedFailure() {
    Object o = null;
    o.toString();
}

for older versions of JUnit:

public void testExpectedFailure() {
    try {
        Object o = null;
        o.toString();
        fail("shouldn't get here");
    }
    catch (NullPointerException e) {
        // expected
    }
}

If you have a bunch of things that you want to ensure throw an exception, you may also want to use this second technique inside a loop rather than creating a separate test method for each case. If you were just to loop through a bunch of cases in a single method using expected, the first one to throw an exception would end the test, and the subsequent cases wouldn’t get checked.