public function test_add_vocabulary()
  {
    $vocab_count = count(Vocabulary::list());
    $v = new Vocabulary($this->vocab_name, $this->vocab_desc, Vocabulary::feature_mask(true, false, false, false);
    $v->insert();

    $this->assertEquals($vocab_count + 1, count(Vocabulary::list()));
    $this->assertTrue(in_array($this->vocab_name, Vocabulary::list()));
  }