public function testSortByKeys()
 {
     $array = new ArrayObject();
     $array['key2'] = 'test2';
     $array['key1'] = 'test1';
     $this->assertEquals(new ArrayObject('key2', 'key1'), $array->getKeys());
     $array->sortByKeys();
     $this->assertEquals(new ArrayObject('key1', 'key2'), $array->getKeys());
 }