}

  public void testSkipNulls() {
    Joiner skipNulls = J.skipNulls();
    checkNoOutput(skipNulls, iterable);
    checkNoOutput(skipNulls, iterableNull);
    checkNoOutput(skipNulls, iterableNullNull);
    checkNoOutput(skipNulls, iterableFourNulls);
    checkResult(skipNulls, iterable1, "1");
    checkResult(skipNulls, iterable12, "1-2");
    checkResult(skipNulls, iterable123, "1-2-3");

   *   <li>Inequality check is not performed against state mutation methods such as {@link
   *       List#add}, or functional update methods such as {@link
   *       com.google.common.base.Joiner#skipNulls}.
   * </ul>
   *
   * <p>Note that constructors taking a builder object cannot be tested effectively because
   * semantics of builder can be arbitrarily complex. Still, a factory class can be created in the

   *   <li>Inequality check is not performed against state mutation methods such as {@link
   *       List#add}, or functional update methods such as {@link
   *       com.google.common.base.Joiner#skipNulls}.
   * </ul>
   *
   * <p>Note that constructors taking a builder object cannot be tested effectively because
   * semantics of builder can be arbitrarily complex. Still, a factory class can be created in the