* MD5 (128 hash bits) hash function and the given secret key.
   *
   * <p>If you are designing a new system that needs HMAC, prefer {@link #hmacSha256} or other
   * future-proof algorithms <a
   * href="https://datatracker.ietf.org/doc/html/rfc6151#section-2.3">over {@code hmacMd5}</a>.
   *
   * @param key the secret key

   */
  protected void verify(List<E> elements) {}

  /** Executes the test. */
  @SuppressWarnings("CatchingUnchecked") // sneaky checked exception
  public final void test() {
    try {
      recurse(0);
    } catch (Exception e) { // sneaky checked exception
      throw new RuntimeException(Arrays.toString(stimuli), e);
    }
  }

  public void testForEachRemaining() {

  @SuppressWarnings("CatchingUnchecked") // sneaky checked exception
  public final void test() {
    try {
      recurse(0);
    } catch (Exception e) { // sneaky checked exception
      throw new RuntimeException(Arrays.toString(stimuli), e);
    }
  }

  private void recurse(int level) {
    // We're going to reuse the stimuli array 3^steps times by overwriting it
    // in a recursive loop.  Sneaky.

   * combinations of methods, then checks compare(), binarySearch() and so
   * forth on each one.
   */

  // should periodically try increasing this, but it makes the test run long
  private static final int RECURSE_DEPTH = 2;

  public void testCombinationsExhaustively_startingFromNatural() {
    testExhaustively(Ordering.<String>natural(), "a", "b", "d");
  }

  @GwtIncompatible // too slow

   * combinations of methods, then checks compare(), binarySearch() and so
   * forth on each one.
   */

  // should periodically try increasing this, but it makes the test run long
  private static final int RECURSE_DEPTH = 2;

  public void testCombinationsExhaustively_startingFromNatural() {
    testExhaustively(Ordering.<String>natural(), "a", "b", "d");
  }

  @GwtIncompatible // too slow

  public static final String UPGRADE = "Upgrade";
  /**
   * The HTTP <a href="https://w3c.github.io/webappsec-upgrade-insecure-requests/#preference">{@code
   * Upgrade-Insecure-Requests}</a> header field name.
   *
   * @since 28.1
   */
  public static final String UPGRADE_INSECURE_REQUESTS = "Upgrade-Insecure-Requests";

  /** The HTTP {@code User-Agent} header field name. */
  public static final String USER_AGENT = "User-Agent";

   * comparator to look for it wherever it wants.
   *
   * Note that we do NOT touch the comparator returned by comparator(), which
   * should be identical to the one the user passed in. We touch only the
   * "secret" comparator used by the delegate implementation.
   */

  private static <K, V> SortedMap<K, V> newModifiableDelegate(Comparator<? super K> comparator) {
    return newTreeMap(nullAccepting(comparator));
  }