String categoryId = PropertyHelper.getPropertyId("category1", null);
Predicate predicate = new CategoryIsEmptyPredicate(categoryId);
Assert.assertTrue(predicate.evaluate(resource));
resource.addCategory(categoryId);
Assert.assertTrue(predicate.evaluate(resource));
String propertyId = PropertyHelper.getPropertyId("category1", "bar");
resource.setProperty(propertyId, "value1");
Assert.assertFalse(predicate.evaluate(resource));