extends AbstractMap<K, V> implements Serializable {
  /*
   * TODO: Make this a drop-in replacement for j.u. versions, actually drop them in, and test the
   * world. Figure out what sort of space-time tradeoff we're actually going to get here with the
   * *Map variants. This class is particularly hard to benchmark, because the benefit is not only in
   * less allocation, but also having the GC do less work to scan the heap because of fewer

 */
@GwtCompatible
@NullMarked
public class UnmodifiableCollectionTests {

  public static void assertMapEntryIsUnmodifiable(Entry<?, ?> entry) {
    try {
      // fine because the call is going to fail without modifying the entry
      @SuppressWarnings("unchecked")
      Entry<?, @Nullable Object> nullableValueEntry = (Entry<?, @Nullable Object>) entry;
      nullableValueEntry.setValue(null);

    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.
    if (level == stimuli.length) {
      // We've filled the array.
      compareResultsForThisListOfStimuli();
    } else {

        assertEquals(expectedElements, targetElements);
      } else {
        assertEqualIgnoringOrder(expectedElements, targetElements);
      }
    }
  }

  private void recurse(int level) {
    // We're going to reuse the stimuli array 3^steps times by overwriting it
    // in a recursive loop.  Sneaky.
    if (level == stimuli.length) {
      // We've filled the array.
      compareResultsForThisListOfStimuli();
    } else {

       */
      ignoredMembers.add(Converter.class.getMethod("apply", Object.class));
    } catch (NoSuchMethodException shouldBeImpossible) {
      // Fine: If it doesn't exist, then there's no chance that we're going to be asked to test it.
    }

    /*
     * These methods "should" call checkNotNull. However, I'm wary of accidentally introducing

    routes have failed but this is no exposed in the API.

 *  **ResponseSource is gone.** This enum exposed whether a response came from
    the cache, network, or both. OkHttp 2 offers more detail with raw access to
    the cache and network responses in the new `Response` class.

 *  **TunnelRequest is gone.** It specified how to connect to an HTTP proxy.
    OkHttp 2 uses the new `Request` class for this.

   * methods as implementations of normal converters do?
   *
   * But no matter what we do, it's worth remembering that the resulting code is going to be unsound
   * in the presence of LegacyConverter, at least in the case of users who view the converter as a
   * Function<A, B> or who call convertAll (and for any checkers that apply @PolyNull-like semantics

   *     {@code off + len} is greater than {@code b.length}
   */
  @CanIgnoreReturnValue
  // Sometimes you don't care how many bytes you actually read, I guess.
  // (You know that it's either going to read len bytes or stop at EOF.)
  public static int read(InputStream in, byte[] b, int off, int len) throws IOException {
    checkNotNull(in);
    checkNotNull(b);
    if (len < 0) {

   * }
   */
  private static final SuccessorsFunction<Character> JAVADOC_GRAPH =
      createUndirectedGraph("ba", "ad", "be", "ac", "ec", "cf");

  /**
   * A diamond shaped directed graph (arrows going down):
   *
   * {@snippet :
   *   a
   *  / \
   * b   c
   *  \ /
   *   d
   * }
   */
  private static final SuccessorsFunction<Character> DIAMOND_GRAPH =

   * }
   */
  private static final SuccessorsFunction<Character> JAVADOC_GRAPH =
      createUndirectedGraph("ba", "ad", "be", "ac", "ec", "cf");

  /**
   * A diamond shaped directed graph (arrows going down):
   *
   * {@snippet :
   *   a
   *  / \
   * b   c
   *  \ /
   *   d
   * }
   */
  private static final SuccessorsFunction<Character> DIAMOND_GRAPH =