5519. 'By this I shall know that you are upright men' means its willingness, provided that they were not interested in truths for the sake of gain. This is clear from the meaning of 'knowing' here as being willing, for the train of thought leads on to this; and from the meaning of 'that you are upright men', and so not spies, as people whose interest in truths was not for the sake of gain, dealt with in 5432, 5512.