Confused about 'respond_to' vs 'respond_to?'

Question

I am learning Rails with railstutorial.org, and I am confused about something: in this chapter the author tells us to do some testing in the console with the respond_to?

Answer 1

The test uses convenient helpers to be more user friendly.

Ruby is Ruby so using the good old respond_to? would work if you call it this way:

 @user.respond_to?(:encrypted_password).should be_true

There is another respond_to used in controllers but still nothing to do with those you already met.