code: public final <S extends Subject<S, A>, A> SimpleSubjectBuilder<S, A> about(
        Subject.Factory<S, A> factory) {
      return new SimpleSubjectBuilder<>(metadata(), factory);
    }
docs: Given a factory for some {@code Subject} class, returns a builder whose {@code that(actual)}
  method creates instances of that class. Created subjects use the previously set failure
  strategy and any previously set failure message.