@Test
    void testNotItem() {
        NotItem n = new NotItem();

        n.addNegativeItem(new WordItem("notthis"));
        n.addNegativeItem(new WordItem("andnotthis"));
        n.addPositiveItem(new WordItem("butthis"));
        assertEquals("+butthis -notthis -andnotthis", n.toString());
    }
<p>Tests that the correct query language strings are generated for various
query trees.</p>

<p>The opposite direction is tested by
{@link com.yahoo.prelude.query.parser.test.ParseTestCase}.
Note that the query language statements produced by a query tree is a
subset of the statements accepted by the parser.</p>

@author bratseth
container-search/src/test/java/com/yahoo/prelude/query/test/QueryLanguageTestCase.java