* intermediate zero-state. Ways we could deal with this are:
   *
   * - Don't define any of the ConcurrentMap operations. This is the current state of affairs.
   *
   * - Define putIfAbsent and replace as treating zero and absent identically (as currently
   *   implemented below). This is a bit surprising with putIfAbsent, which really becomes
   *   putIfZero.

  public void testPutIfAbsent_supportedAbsent() {
    assertNull(
        "putIfAbsent(notPresent, value) should return null", getMap().putIfAbsent(k3(), v3()));
    expectAdded(e3());
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_supportedPresent() {
    assertEquals(
        "putIfAbsent(present, value) should return existing value",
        v0(),

    assertNull("putIfAbsent(notPresent, value) should return null", putIfAbsent(e3()));
    expectAdded(e3());
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_supportedPresent() {
    assertEquals(
        "putIfAbsent(present, value) should return existing value",
        v0(),
        getMap().putIfAbsent(k0(), v3()));
    expectUnchanged();
  }

    assertNull("putIfAbsent(notPresent, value) should return null", putIfAbsent(e3()));
    expectAdded(e3());
  }

  @MapFeature.Require(SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_supportedPresent() {
    assertEquals(
        "putIfAbsent(present, value) should return existing value",
        v0(),
        getMap().putIfAbsent(k0(), v3()));
    expectUnchanged();
  }

    // since get returned null, try a putIfAbsent; that fails due to a simulated race
    when(backingMap.putIfAbsent(eq(KEY), isA(AtomicInteger.class))).thenReturn(existingZero);
    // since the putIfAbsent returned a zero, we'll try to replace...
    when(backingMap.replace(eq(KEY), eq(existingZero), isA(AtomicInteger.class))).thenReturn(false);
    // ...and then putIfAbsent. Simulate failure on both

    for (int i = 0; i < ITERATIONS; i++) {
      long before = map.get(key);
      long result = map.putIfAbsent(key, newValue);
      long after = map.get(key);
      assertEquals(before, result);
      assertEquals(before == 0 ? newValue : before, after);

      map.remove(key);
      before = map.get(key);
      result = map.putIfAbsent(key, newValue);
      after = map.get(key);
      assertEquals(0, before);

    }

    private static List<String> visitAll(
            Collection<Vertex> children, Map<Vertex, DfsState> stateMap, List<String> list) {
        for (Vertex v : children) {
            DfsState state = stateMap.putIfAbsent(v, DfsState.VISITING);
            if (state == null) {
                visitAll(v.children, stateMap, list);
                stateMap.put(v, DfsState.VISITED);
                list.add(v.label);
            }
        }

      entryArray[i] = e;
      V oldValue = forwardDelegate.putIfAbsent(e.getKey(), e.getValue());
      if (oldValue != null) {
        throw conflictException("key", e.getKey() + "=" + oldValue, entryArray[i]);
      }
      K oldKey = backwardDelegate.putIfAbsent(e.getValue(), e.getKey());
      if (oldKey != null) {

    }
  }

  public void testPutIfAbsent() {
    TestMap map = new TestMap();
    map.put("foo", 1);
    assertEquals(Integer.valueOf(1), map.putIfAbsent("foo", 2));
    assertEquals(Integer.valueOf(1), map.get("foo"));
    assertNull(map.putIfAbsent("bar", 3));
    assertEquals(Integer.valueOf(3), map.get("bar"));
  }

  public void testRemove() {
    TestMap map = new TestMap();
    map.put("foo", 1);

    }

    private static List<String> visitAll(
            Collection<Vertex> children, Map<Vertex, DfsState> stateMap, List<String> list) {
        for (Vertex v : children) {
            DfsState state = stateMap.putIfAbsent(v, DfsState.VISITING);
            if (state == null) {
                visitAll(v.children, stateMap, list);
                stateMap.put(v, DfsState.VISITED);
                list.add(v.label);
            }
        }