Asserting Nullness

• public static void assertNull(Object o)

• public static void assertNull(String message, Object o)

e.g. testing for memory leak:

    public void testMemoryLeak() throws InterruptedException {
        Fraction a = Fraction.getFraction(1, 2);
        WeakReference ref = new WeakReference(a);
        a = null;
        System.gc();
        System.gc();
        System.gc();
        Thread.sleep(1000);
        assertNull(ref.get());
    }