public function testCanOverrideInvalidRelation()
 {
     $args = array('type' => 'taxonomy', 'taxonomy' => 'category', 'relation' => 'IN');
     $f = new Field($args);
     $defaults = $f->getDefaults();
     $default_relation = $defaults['relation'];
     $this->assertTrue($f->getRelation() == $default_relation);
 }