(a, b) -> {
          count.incrementAndGet();
          assertThat(a.equals(String.valueOf(b))).isTrue();
        });
    assertThat(count.get()).isEqualTo(100000);
    // of course, this test doesn't prove that anything actually happened in parallel...
  }

  // TODO(kevinb): switch to importing Truth's assertThat(DoubleStream) if we get that added
  private static IterableSubject assertThatDoubleStream(DoubleStream stream) {