checkUnmodifiableMultimap(
        synchronizedSetMultimap(HashMultimap.<@Nullable String, @Nullable Integer>create()), false);
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testSerializingUnmodifiableSynchronizedHashMultimap() {
    Multimap<String, Integer> unmodifiable =
        prepareUnmodifiableTests(

   * {@code map} and the instances generated by {@code factory} are. Concurrent read operations will
   * work correctly. To allow concurrent update operations, wrap the multimap with a call to {@link
   * #synchronizedSetMultimap}.
   *
   * <p>Call this method only when the simpler methods {@link HashMultimap#create()}, {@link
   * LinkedHashMultimap#create()}, {@link TreeMultimap#create()}, and {@link