public function test_lock()
 {
     $this->assertTrue($this->store->acquire_lock('lock', '123'));
     $this->assertTrue($this->store->check_lock_state('lock', '123'));
     $this->assertFalse($this->store->check_lock_state('lock', '321'));
     $this->assertNull($this->store->check_lock_state('notalock', '123'));
     $this->assertFalse($this->store->release_lock('lock', '321'));
     $this->assertTrue($this->store->release_lock('lock', '123'));
 }