Collection::keys PHP Метод

    public function keys()
    {
        return array_keys($this->data);
    }

 public function test_getting_array_of_keys()
 {
     $coll = new Collection();
     $coll->addItem('Test Item', 1);
     $coll->addItem('Test Item', 2);
     $actual = $coll->keys();
     $expected = array(1, 2);
     $this->assertEquals($expected, $actual);
 }