@Test
public void testClear() throws Exception {

    final GrammarDocument document = new ExternalGrammarDocument(null,
            null, null, true);
    storage.addGrammarDocument("12345", document);
    final URI uri = document.getURI();
    Assert.assertNotNull(uri);
    Assert.assertEquals(document, storage.getDocument(uri));
    storage.clear("12345");
    Assert.assertNull("document not cleared", storage.getDocument(uri));
}