@CollectionSize.Require(absent = ZERO)
  public void testRemove_present() {
    int initialSize = collection.size();
    assertTrue("remove(present) should return true", collection.remove(e0()));
    assertEquals(
        "remove(present) should decrease a collection's size by one.",
        initialSize - 1,
        collection.size());
    expectMissing(e0());
  }

  @CollectionSize.Require(absent = ZERO)
  public void testComputeIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "computeIfAbsent(present, returnsCurrentValue) should return present or throw",
          v0(),
          getMap()
              .computeIfAbsent(
                  k0(),
                  k -> {
                    assertEquals(k0(), k);

        Entry<E> result = wrapEntry(requireNonNull(current));
        prevEntry = result;
        if (current.succ() == header) {
          current = null;
        } else {
          current = current.succ();
        }
        return result;
      }

      @Override
      public void remove() {
        checkState(prevEntry != null, "no calls to next() since the last call to remove()");

          };
    }
    Iterator<Entry<K, V>> entryItr = navigableMap.entrySet().iterator();
    Entry<K, V> prevEntry = entryItr.next();
    while (entryItr.hasNext()) {
      Entry<K, V> nextEntry = entryItr.next();
      assertTrue(comparator.compare(prevEntry.getKey(), nextEntry.getKey()) < 0);
      prevEntry = nextEntry;
    }
  }

  @CollectionSize.Require(absent = ZERO)
  public void testComputeIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "computeIfAbsent(present, returnsCurrentValue) should return present or throw",
          v0(),
          getMap()
              .computeIfAbsent(
                  k0(),
                  k -> {
                    assertEquals(k0(), k);

  }

  @MapFeature.Require({SUPPORTS_PUT, SUPPORTS_REMOVE})
  @CollectionSize.Require(absent = ZERO)
  public void testCompute_presentToPresent() {
    assertEquals(
        "Map.compute(present, functionReturningValue) should return new value",
        v3(),
        getMap()
            .compute(
                k0(),
                (k, v) -> {
                  assertEquals(k0(), k);

  }

  @MapFeature.Require({SUPPORTS_PUT, SUPPORTS_REMOVE})
  @CollectionSize.Require(absent = ZERO)
  public void testCompute_presentToPresent() {
    assertEquals(
        "Map.compute(present, functionReturningValue) should return new value",
        v3(),
        getMap()
            .compute(
                k0(),
                (k, v) -> {
                  assertEquals(k0(), k);

  /**
   * Removes {@code node} if it is present; all edges incident to {@code node} will also be removed.
   *
   * @return {@code true} if the network was modified as a result of this call
   */
  @CanIgnoreReturnValue
  boolean removeNode(N node);

  /**
   * Removes {@code edge} from this network, if it is present.
   *

  @MapFeature.Require(absent = SUPPORTS_PUT)
  @CollectionSize.Require(absent = ZERO)
  public void testPutIfAbsent_unsupportedPresentExistingValue() {
    try {
      assertEquals(
          "putIfAbsent(present, existingValue) should return present or throw",
          v0(),
          putIfAbsent(e0()));
    } catch (UnsupportedOperationException tolerated) {
    }
    expectUnchanged();
  }

  @MapFeature.Require(absent = SUPPORTS_PUT)

        return map.containsKey(o);
    }

    @Override
    public boolean add(final String o) {
        return map.put(o, PRESENT) == null;
    }

    @Override
    public boolean remove(final Object o) {
        return map.remove(o) == PRESENT;
    }

    @Override
    public void clear() {
        map.clear();
    }