/**
  * popAtomic should not call the callback if there are no messages
  */
 public function testPopAtomicEmpty()
 {
     $did_run = false;
     $callback = function ($unused) use(&$did_run) {
         $did_run = true;
     };
     $data = $this->object->popAtomic($callback);
     $this->assertNull($data, 'Should return null on an empty queue');
     $this->assertFalse($did_run, 'Should not call callback without a message');
 }