The nature of the test, which despite the presence of a boatload of silver has nothing to do with money, was this: Nostromo had to choose between personal integrity -- his 'selfish' reputation, which he could maintain by choosing the mission -- and providing for Teresa's need of a priest -- a need which has no meaning to him, but every meaning to her, making that choice truly 'selfless.' By failing the test, Nostromo preserves his self.