Collection::map PHP Method

    public function map($callback)
    {
        $this->data = array_map($callback, $this->data);
        return $this;
    }

 public function testMap()
 {
     $this->collection->map(function ($item) {
         return sprintf('%s %s', $item['first_name'], $item['last_name']);
     });
     $this->assertEquals(['john smith', 'kara trace', 'phil mcKay', 'rose smith'], $this->collection->toArray());
 }