assertEquals(expected.length == 0, source.isEmpty());
  }

  public void testSize() throws IOException {
    assertEquals(expected.length, source.size());
  }

  public void testSizeIfKnown() throws IOException {
    Optional<Long> sizeIfKnown = source.sizeIfKnown();
    if (sizeIfKnown.isPresent()) {
      assertEquals(expected.length, (long) sizeIfKnown.get());
    }
  }