public function testChunk()
 {
     $collection = new Collection(['a', 'b', 'c', 'd']);
     $this->assertEquals([new Collection(['a', 'b', 'c']), new Collection(['d'])], $collection->chunk(3));
     $this->assertEquals([new Collection(['a', 'b']), new Collection(['c', 'd'])], $collection->chunk(2));
     $this->assertEquals([new Collection(['a', 'b', 'c', 'd'])], $collection->chunk(5));
 }