public function testFilter()
 {
     $resultSet = new ResultSet([['key' => 1], ['key' => 2], ['key' => 3]]);
     $results = $resultSet->filter(function ($item) {
         return $item['key'] > 1;
     });
     $this->assertEquals(3, count($resultSet));
     $this->assertEquals(3, $resultSet[2]['key']);
     $this->assertInstanceOf('\\Reach\\ResultSet', $results);
     $this->assertEquals(2, count($results));
     $this->assertEquals(2, $results[0]['key']);
     $this->assertEquals(3, $results[1]['key']);
 }