How to catch a liar

A man and his friend went to a bar and started talking. The man says to his friend “I think my wife is cheating on me.”

The friend says, “How do you know?”
The man replies, “She didn’t come home last night and she said she was with her sister Shirley.”
The friend said, “and…..”
The man says, “She is lying because I was with her sister last night.”