Reduced to essence: When Abigail is finally directly challenged at the court by Mary Warren's confession and John Proctor's confession, she exposes her truest self. She lies and she lies very convincingly. Abigail, reduced to her final defense, is seen as a manipulator who is incapable of putting herself at risk. Her dishonesty is thorough and this is made clear by her response to extreme circumstances.
Severe Test: John Proctor confesses adultery in public, sacrificing his great pride in an effort to save his wife. He is later tempted with an offer to save his own life by signing a false confession which would condemn others to certain death. He is brought low by his plight, at points nearly giving in to despair and self-effacement. He does not believe that he is good enough to meet the challenge that faces him, which is, ultimately, a challenge to his integrity.
After having made mistakes (adultery), Proctor worries that his true nature is weakness. Yet, in the end, he is shown to be strong. He needs the help of Elizabeth to see himself as a good and strong person, but he comes to see that he can grasp his final chance at integrity and he does.