Final answer:
Malcolm tests Macduff's loyalties by equivocating about his own character, claiming to be a worse tyrant than Macbeth; Macduff's shocked response proves his true opposition to Macbeth.
Step-by-step explanation:
In William Shakespeare's Macbeth, Malcolm uses equivocation as a test to ensure Macduff's loyalties do not align with Macbeth's.
This occurs in Act 4, Scene 3, when Malcolm pretends to be even more villainous than Macbeth in order to provoke a reaction from Macduff.
By claiming he would commit atrocities if he were king, Malcolm observes Macduff's response to determine whether he is truly against Macbeth or if he is trying to entrap Malcolm.
Macduff's reaction, one of shock and dismay, convinces Malcolm that Macduff's intentions are genuine and that he truly opposes Macbeth's tyranny.