How do you ensure other methods are not called?

This is kind of reverse thinking...but hopefully you understand what I'm trying to verify.

I have a 'helper class' that has 4 public methods. Each of these methods are a variation of arguments that call a single private method.

What I'm trying to mock is that each of these 4 public methods only makes a single call to the expected method. Recording the call that is expected is the easy part...but how do I ensure no further calls to some other private method that may exist there in the future isn't called?

Make sense?