} while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, stack, null));

      RunnableExecutorPair reversedStack = null;
      while (stack != NULL_PAIR) {
        RunnableExecutorPair head = stack;
        stack = stack.next;
        head.next = reversedStack;
        reversedStack = head;
      }
      stack = reversedStack;
      while (stack != null) {
        stack.execute();
        stack = stack.next;
      }

  public void testSingleTearDown() throws Exception {
    final TearDownStack stack = buildTearDownStack();

    final SimpleTearDown tearDown = new SimpleTearDown();
    stack.addTearDown(tearDown);

    assertEquals(false, tearDown.ran);

    stack.runTearDown();

    assertEquals("tearDown should have run", true, tearDown.ran);
  }

        }
        return pop(stack);
      }

      <E extends @Nullable Object> void push(List<E> stack, E value) {
        stack.add(value);
      }

      <E extends @Nullable Object> E pop(List<E> stack) {
        return stack.remove(stack.size() - 1);
      }
    };

    abstract <T extends @Nullable Object, A extends @Nullable Object, R extends @Nullable Object>

      } while (!UNSAFE.compareAndSwapObject(this, HEAD_OFFSET, stack, null));

      RunnableExecutorPair reversedStack = null;
      while (stack != NULL_PAIR) {
        RunnableExecutorPair head = stack;
        stack = stack.next;
        head.next = reversedStack;
        reversedStack = head;
      }
      stack = reversedStack;
      while (stack != null) {
        stack.execute();
        stack = stack.next;
      }

                    }
                  },
                  service);
        } else if (i % DIRECT_EXECUTIONS_PER_THREAD == DIRECT_EXECUTIONS_PER_THREAD - 1) {
          // When at max depth, record stack trace depth
          lengthChecks.add(
              serializer.submit(
                  new Callable<Integer>() {
                    @Override
                    public Integer call() {

                    }
                  },
                  service);
        } else if (i % DIRECT_EXECUTIONS_PER_THREAD == DIRECT_EXECUTIONS_PER_THREAD - 1) {
          // When at max depth, record stack trace depth
          lengthChecks.add(
              serializer.submit(
                  new Callable<Integer>() {
                    @Override
                    public Integer call() {

    // TODO: verify contents afterward
    // TODO: something shiny and new instead of Stack
    // TODO: test whether null is supported (create a Feature)
    /**
     * The elements to be returned by future calls to {@code next()}, with the first at the top of
     * the stack.
     */
    final Stack<E> nextElements = new Stack<>();

    /**

    }
  }

  /**
   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
   * {@link Throwable#getStackTrace()}.
   */
  @GwtIncompatible // java.io.PrintWriter, java.io.StringWriter

    }
  }

  /**
   * Returns a string containing the result of {@link Throwable#toString() toString()}, followed by
   * the full, recursive stack trace of {@code throwable}. Note that you probably should not be
   * parsing the resulting string; if you need programmatic access to the stack frames, you can call
   * {@link Throwable#getStackTrace()}.
   */
  @GwtIncompatible // java.io.PrintWriter, java.io.StringWriter

          ImmutableList.of(1, 2),
          ImmutableList.of(3, 5),
          ImmutableList.of(2, 4),
          ImmutableList.of(1, 2, 3, 5, 6, 8, 9));

  /*
   * We have a whole series of abstract test classes that "stack", so e.g. the tests for filtered
   * NavigableSets inherit the tests for filtered Iterables, Collections, Sets, and SortedSets. The
   * actual implementation tests are further down.
   */