assertEquals(expected.length(), source.length());
  }

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

  public void testReadLines_withProcessor() throws IOException {
    List<String> list =
        source.readLines(