Actually, that’s not a great analogy. If the cop who pulled you over doesn’t testify, you have a very good chance of going free.
But if the cop pulled you over because someone reported you for swerving all over the road, and you blow a 0.20 on your DUI test, and you say, “But you can’t convict me because I didn’t hit anyone, and anyway I demand to confront the person who called 911 on me,” the judge will laugh in your face.