public function testundo()
{
$my_string = "Is your name O'reilly?";
$string = new williamknauss\String($my_string);
$string->addslashes();
$string->undo();
//assert 1
$this->assertEquals($my_string, $string->__toString());
$my_string = " Hello World";
$string = new williamknauss\String($my_string);
$string->trim()->str_replace("Hello", "Goodbye")->str_replace("World", "Planet")->undo()->undo()->undo();
//assert 2
$this->assertEquals($my_string, $string->__toString());
}