@Test
    void testDocumentFrequency() {
        Query q = new Query("?query=a%20b");
        CompositeItem root = (CompositeItem) q.getModel().getQueryTree().getRoot();
        ((WordItem) root.getItem(0)).setDocumentFrequency(new DocumentFrequency(13, 100));
        ((WordItem) root.getItem(1)).setDocumentFrequency(new DocumentFrequency(14, 110));;
        q.prepare();
        assertEquals("13", q.getRanking().getProperties().get("vespa.term.1.docfreq").get(0));
        assertEquals("100", q.getRanking().getProperties().get("vespa.term.1.docfreq").get(1));
        assertEquals("14", q.getRanking().getProperties().get("vespa.term.2.docfreq").get(0));
        assertEquals("110", q.getRanking().getProperties().get("vespa.term.2.docfreq").get(1));
    }
Tests that significance is transferred to rank properties by preparing the query
(which strictly is an implementation detail which we should rather hide).
container-search/src/test/java/com/yahoo/prelude/query/test/QueryCanonicalizerTestCase.java