long estimatedSize = 0L;
    ImmutableList.Builder<Spliterator.OfDouble> splitrsBuilder =
        new ImmutableList.Builder<>(streams.length);
    for (DoubleStream stream : streams) {
      isParallel |= stream.isParallel();
      Spliterator.OfDouble splitr = stream.spliterator();
      splitrsBuilder.add(splitr);
      characteristics &= splitr.characteristics();

                    Spliterator.SIZED | Spliterator.DISTINCT | Spliterator.NONNULL,
                    4))
        .expect(1L, 1L, 2L, 3L);
  }

  public void testFlatMapToDouble_nullStream() {
    SpliteratorTester.ofDouble(
            () ->
                CollectSpliterators.flatMapToDouble(
                    Arrays.spliterator(new Double[] {1.0, 0.0, 1.0, 2.0, 3.0}),

      return false;
    }

    @Override
    public Double get(int index) {
      checkElementIndex(index, size());
      return array[start + index];
    }

    @Override
    public Spliterator.OfDouble spliterator() {
      return Spliterators.spliterator(array, start, end, 0);
    }

    @Override
    public boolean contains(@Nullable Object target) {
      // Overridden to prevent a ton of boxing