Writer writer = new AppendableWriter(builder);

    writer.append("Hello,");
    writer.append(' ');
    writer.append("The World Wide Web", 4, 9);
    writer.append("!");

    assertEquals("Hello, World!", builder.toString());
  }

  public void testCloseFlush() throws IOException {
    SpyAppendable spy = new SpyAppendable();
    Writer writer = new AppendableWriter(spy);

    writer.write("Hello");

   */
  public static Writer asWriter(Appendable target) {
    if (target instanceof Writer) {
      return (Writer) target;
    }
    return new AppendableWriter(target);
  }