public function testCanSetMultipleValuesForSameAttribute()
 {
     $expected = "<h1 class='one two'>{$this->testContent}</h1>";
     $el = new HTMLElement();
     $el->setNodeType('h1');
     $el->setContent($this->testContent);
     $el->class = 'one';
     $el->setAttribute('class', 'two');
     $this->assertEquals($expected, $el->getNode());
 }