private static <K, V>
      Correspondence<SetMultimap<K, V>, SetMultimap<K, String>> setMultimapValuesByString() {
    return Correspondence.from(
        (actual, expected) ->
            ImmutableSetMultimap.copyOf(transformValues(actual, Object::toString)).equals(expected),
        "is equivalent comparing multimap values by `toString()` to");
  }
Report an error for any class annotated.
common/src/test/java/com/google/auto/common/BasicAnnotationProcessorTest.java