Readers, of course, know that Johnny is telling the truth (and in the case of his mother’s story, what he believes is the truth) about not stealing the cup. Isannah’s testimony, however, is questionable—recall that she was asleep when Johnny showed Cilla the cup, so it seems likely that she was coached to back Cilla up. However, Johnny is in the right in this instance, so it’s not a negative thing that Rab and Mr. Quincy brought forth a witness who wasn’t actually there—they’re fighting for the right thing, so the novel casts their methods as justified and forgivable.