What "validation logic" I should test?
I am using Ruby on Rails 3.0.9 and RSpec 2. I would like to know what "validation logic" I should test. That is, if in my model I have:

    class User < ActiveRecord::Base
      validates :firstname
        :presence => true
    end

**What should I test of the following?**

 1. "should have a valid first name"
 2. "should not have a valid first name"

**Or should I test both?**
What "validation logic" I should test?
===

I am using Ruby on Rails 3.0.9 and RSpec 2. I would like to know what "validation logic" I should test. That is, if in my model I have:

    class User < ActiveRecord::Base
      validates :firstname
        :presence => true
    end

**What should I test of the following?**

 1. "should have a valid first name"
 2. "should not have a valid first name"

**Or should I test both?**