public function testDefaultConfigMerging()
 {
     $this->assertEquals('foo', HTML_QuickForm2_Rule::mergeConfig('foo', null));
     $this->assertEquals('bar', HTML_QuickForm2_Rule::mergeConfig('foo', 'bar'));
     HTML_QuickForm2_Factory::registerRule('no-config', 'HTML_QuickForm2_Rule_ImplConst');
     HTML_QuickForm2_Factory::registerRule('with-config', 'HTML_QuickForm2_Rule_ImplConst', null, 'bar');
     $el = new HTML_QuickForm2_Element_InputText();
     $this->assertEquals('foo', $el->createRule('no-config', '', 'foo')->getConfig());
     $this->assertEquals('bar', $el->createRule('with-config', '', 'foo')->getConfig());
 }