why does malcolm test macduff

Outside King Edward’s palace, Malcolm speaks with Macduff, telling him that he does not trust him since he has left his family in Scotland and may be secretly working for Macbeth. To determine whether Macduff is trustworthy, Malcolm rambles on about his own vices. He admits that he wonders whether he is fit to be king, since he claims to be lustful, greedy, and violent. At first, Macduff politely disagrees with his future king, but eventually Macduff cannot keep himself from crying out, “O Scotland, Scotland!” (4.3.101).

what all does macuff say that proove him to be a loyal person