String testString = "abcdefgh";
    CharSource source = newCharSource(testString);
    Reader joinedReader = CharSource.concat(source, source).openStream();

    String expectedString = testString + testString;
    assertThat(CharStreams.toString(joinedReader)).isEqualTo(expectedString);
  }

  private static CharSource newCharSource(String text) {
    return new CharSource() {
      @Override