public function get_key($s, $key, $val)
 {
     $at1 = new stack_cas_casstring($s);
     $this->assertEquals($key, $at1->get_key());
     $this->assertEquals($s, $at1->get_raw_casstring());
     // Note the difference between the two!
     $this->assertEquals($val, $at1->get_casstring());
 }