public function testEvery()
 {
     $data = new Collection([6 => 'a', 4 => 'b', 7 => 'c', 1 => 'd', 5 => 'e', 3 => 'f']);
     $this->assertEquals(['a', 'e'], $data->every(4)->all());
     $this->assertEquals(['b', 'f'], $data->every(4, 1)->all());
     $this->assertEquals(['c'], $data->every(4, 2)->all());
     $this->assertEquals(['d'], $data->every(4, 3)->all());
 }