What confession does Proctor make in open court? How does Danforth test the truth of this confession? What is the ironic result?

John Proctor confesses his affair with Abigail. Danforth asks for Elizabeth Proctor to confirm or deny this without knowing that John has already confessed. The result is ironic because for perhaps the first time in her life, she lies to protect her husband. She then finds out he had already made his confession.