"estimated size of trySplit result (%s) is larger than original size (%s)",
                trySplit.estimateSize(), originalSize));
      }
    }
    if (subsized) {
      if (trySplit != null) {
        assertEquals(
            "sum of estimated sizes of trySplit and original spliterator after trySplit",
            originalSize,
            trySplit.estimateSize() + spliterator.estimateSize());
      } else {

                "estimated size of trySplit result (%s) is larger than original size (%s)",
                trySplit.estimateSize(), originalSize));
      }
    }
    if (subsized) {
      if (trySplit != null) {
        assertEquals(
            "sum of estimated sizes of trySplit and original spliterator after trySplit",
            originalSize,
            trySplit.estimateSize() + spliterator.estimateSize());
      } else {

      this.fromSpliterator = fromSpliterator;
      this.index = index;
    }

    abstract S createSplit(F from, long i);

    @Override
    @CheckForNull
    public S trySplit() {
      Spliterator<?> splitOrNull = fromSpliterator.trySplit();
      if (splitOrNull == null) {
        return null;
      }
      @SuppressWarnings("unchecked")
      F split = (F) splitOrNull;
      S result = createSplit(split, index);

      this.fromSpliterator = fromSpliterator;
      this.index = index;
    }

    abstract S createSplit(F from, long i);

    @Override
    @CheckForNull
    public S trySplit() {
      Spliterator<?> splitOrNull = fromSpliterator.trySplit();
      if (splitOrNull == null) {
        return null;
      }
      @SuppressWarnings("unchecked")
      F split = (F) splitOrNull;
      S result = createSplit(split, index);

            .put(2, 2)
            .put(3, 3)
            .put(4, 4)
            .put(5, 5)
            .put(6, 6)
            .buildOrThrow();
    assertNotNull(map.keySet().spliterator().trySplit());
  }

  public void testEquals() {
    new EqualsTester()
        .addEqualityGroup(
            ImmutableMap.of(),
            ImmutableMap.builder().buildOrThrow(),