}
      return true;
    }

    @Override
    public Optional<Long> lengthIfKnown() {
      long result = 0L;
      for (CharSource source : sources) {
        Optional<Long> lengthIfKnown = source.lengthIfKnown();
        if (!lengthIfKnown.isPresent()) {
          return Optional.absent();
        }
        result += lengthIfKnown.get();
      }
      return Optional.of(result);
    }

    @Override

    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(