Litmus verse

Today, my co-worker was relating a story about a conversation he had concerning the TNIV translation of the Bible. The girl insisted she shouldn't like the TNIV, but she couldn't remember who had said so or why. She rummaged around the Bible to find one of the verses that would tell her immediately whether the translation was bad or not. When she found it, she said, "Well, I guess it's okay." What is this activity called? Yep. It's a litmus verse.