@Test
    public void testProvided() {
        assertTrue(ConcreteDocumentFactory.getAnnotation("NodeImpl") instanceof NodeImpl);
        assertTrue(ConcreteDocumentFactory.getAnnotation("DocumentImpl") instanceof DocumentImpl);
        assertNotNull(ConcreteDocumentFactory.getAnnotation("artist").getClass().getAnnotation(Generated.class));
        assertNull(ConcreteDocumentFactory.getAnnotation("NodeImpl").getClass().getAnnotation(Generated.class));
        assertNull(ConcreteDocumentFactory.getAnnotation("DocumentImpl").getClass().getAnnotation(Generated.class));
        assertNotNull(ConcreteDocumentFactory.getAnnotation("NodeImplSub").getClass().getAnnotation(Generated.class));
        assertNotNull(ConcreteDocumentFactory.getAnnotation("DocumentImplSub").getClass().getAnnotation(Generated.class));
    }
Packs the given doc to Book
@param d doc, never null
@return a Book object or null if input doc isn't a Book
documentgen-test/src/test/java/com/yahoo/vespa/config/DocumentGenPluginTest.java