public function testFilter()
 {
     $one = $this->createNode();
     $two = $this->createNode();
     $collection = new NodeCollection([$one, $two], FALSE);
     $matches = $collection->filter(function (Node $node) use($one) {
         return $node === $one;
     });
     $this->assertCount(1, $matches);
     $this->assertSame($one, $matches[0]);
 }