final char margedChar = mergeChar(originalChar1, originalChar2);
            if (margedChar != originalChar1) {
                sb.setCharAt(i, margedChar);
                sb.deleteCharAt(i + 1);
            } else {
                final char convertedChar = hankakuKatakanaToZenkakuKatakana(originalChar1);
                if (convertedChar != originalChar1) {
                    sb.setCharAt(i, convertedChar);

    List<Character> chars = charactersOf(builder);
    assertEquals(asList('a', 'b', 'c'), chars);
    builder.append("def");
    assertEquals(asList('a', 'b', 'c', 'd', 'e', 'f'), chars);
    builder.deleteCharAt(5);
    assertEquals(asList('a', 'b', 'c', 'd', 'e'), chars);
  }

  public void testNewArrayListEmpty() {
    @SuppressWarnings("UseCollectionConstructor") // test of factory method