public function testExtractWithoutPreservedKeys()
 {
     $data = array(1 => 'a', 0 => 'b', 'a' => 1, 'b' => 0);
     $collection = new Collection($data);
     $result = $collection->extract(1, 0, false);
     $this->assertInstanceOf(get_class($collection), $result);
     $this->assertSame(array_slice($data, 1, 3, false), (array) $result);
 }