function test_remove_resource_triple()
 {
     $g = new SimpleGraph();
     $g->add_resource_triple('http://example.org/subj', 'http://example.org/pred', 'http://example.org/obj');
     $this->assertEquals(1, count($g->get_triples()));
     $g->remove_resource_triple('http://example.org/subj', 'http://example.org/pred', 'http://example.org/obj');
     $this->assertEquals(0, count($g->get_triples()));
 }