@Test
    final void testSetDocumentFrequency() {
        final PhraseSegmentItem p = new PhraseSegmentItem("farmyards", false, false);
        assertFalse(p.getDocumentFrequency().isPresent());
        p.setDocumentFrequency(new DocumentFrequency(13, 100));
        assertTrue(p.getDocumentFrequency().isPresent());
        assertEquals(new DocumentFrequency(13, 100), p.getDocumentFrequency().get());
    }
Keep CompositeTaggableItem, SimpleTaggableItem and TaggableSegmentItem in
lockstep.

@author <a href="mailto:steinar@yahoo-inc.com">Steinar Knutsen</a>
container-search/src/test/java/com/yahoo/prelude/query/TaggableItemsTestCase.java