title: Running a single validation in Rails
body: <p>I'm sending friends invitations and I want to validate email address using <code>User.validates_format_of :email</code>, except that User.email has a couple of other validations which I'm not really interested in.</p>
  
  <p>So is there a way to run a single validation on a model or check if that specific validation has passed (without doing 
  <code>
  user.errors.include?(validation_message)
  </code>
  )?</p>