anchor.diff:      Expect.isTrue(queue.isEmpty);
   
       testAddAll();
  +    testLengthChanges();
       testLarge();
       testFromListToList();
     }
  
positive.code:     }
  
      for (int i = 1; i <= 10; i++) {
        queue.addFirst(i);
        testLength(10 + i, queue);
      }
  
  
negative.code:     queue.retainAll([1, 3, 5, 7, 9, 10]);  // Remove 2 and 8.
      testLength(17, queue);
  
      queue.removeMatching((x) => x == 7);
      testLength(14, queue);
  
      queue.retainMatching((x) => x != 3);
      testLength(11, queue);
  
      Expect.listEquals([9, 1, 5, 9, 10, 1, 5, 9, 10, 1, 5], queue.toList());
  