Unit tests were never considered a silver bullet. The only thing they do is automatically run specific sanity checks on small subcomponents with everything else

Unit tests were never considered a silver bullet. The only thing they do is automatically run specific sanity checks on small subcomponents with everything else faked out. At best, they are a convenient way to ensure that if an invariant suddenly varies unexpectedly and in an unplanned way... A red flag is thrown into play.