}

  public void testSkipNulls() {
    Joiner skipNulls = J.skipNulls();
    checkNoOutput(skipNulls, ITERABLE_);
    checkNoOutput(skipNulls, ITERABLE_NULL);
    checkNoOutput(skipNulls, ITERABLE_NULL_NULL);
    checkNoOutput(skipNulls, ITERABLE_FOUR_NULLS);
    checkResult(skipNulls, ITERABLE_1, "1");
    checkResult(skipNulls, ITERABLE_12, "1-2");
    checkResult(skipNulls, ITERABLE_123, "1-2-3");

 *
 * <p>Another example is an iterator that skips over null elements in a backing iterator. This could
 * be implemented as:
 *
 * <pre>{@code
 * public static Iterator<String> skipNulls(final Iterator<String> in) {
 *   return new AbstractIterator<String>() {
 *     protected String computeNext() {
 *       while (in.hasNext()) {
 *         String s = in.next();
 *         if (s != null) {

   *       versa.
   *   <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}.
   *   <li>If the constructor or factory method used to construct instance takes a parameter that
   *       {@link AbstractPackageSanityTests} doesn't know how to construct, the test will fail.

   *       versa.
   *   <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}.
   *   <li>If the constructor or factory method used to construct instance takes a parameter that
   *       {@link AbstractPackageSanityTests} doesn't know how to construct, the test will fail.

   *   <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