function test_get_first_literal_uses_preferred_language()
 {
     $g = new SimpleGraph();
     $g->add_literal_triple('http://example.org/subj', 'http://example.org/pred', 'en', 'en');
     $g->add_literal_triple('http://example.org/subj', 'http://example.org/pred', 'fr', 'fr');
     $g->add_literal_triple('http://example.org/subj', 'http://example.org/pred', 'de', 'de');
     $this->assertEquals("en", $g->get_first_literal('http://example.org/subj', 'http://example.org/pred', null, 'en'));
     $this->assertEquals("fr", $g->get_first_literal('http://example.org/subj', 'http://example.org/pred', null, 'fr'));
     $this->assertEquals("de", $g->get_first_literal('http://example.org/subj', 'http://example.org/pred', null, 'de'));
 }