public function testAddUnknownType()
 {
     $c = new HTML_QuickForm2_ContainerImpl('cCOT2');
     try {
         $c->addUnknown('uCOT1');
     } catch (HTML_QuickForm2_InvalidArgumentException $e) {
         $this->assertEquals("Element type 'unknown' is not known", $e->getMessage());
         return;
     }
     $this->fail('Expected HTML_QuickForm2_InvalidArgumentException was not thrown');
 }