}
    assertEquals(expected, builder.toString());
  }

  static final CharSource BROKEN_READ_SOURCE = new TestCharSource("ABC", READ_THROWS);
  static final CharSource BROKEN_CLOSE_SOURCE = new TestCharSource("ABC", CLOSE_THROWS);
  static final CharSource BROKEN_OPEN_SOURCE = new TestCharSource("ABC", OPEN_THROWS);
  static final CharSink BROKEN_WRITE_SINK = new TestCharSink(WRITE_THROWS);