@Override
    public int count(String term) {
        MutableInt count = freq.get(term);
        return count == null ? 0 : count.value;
    }
@Test
    public void testGetBigramFrequency() {
        System.out.println("getBigramFrequency");
        Bigram bigram = new Bigram("romantic", "comedy");
        assertEquals(9, corpus.count(bigram));
    }