Rspec test fails to show that model requires an email

I'm (mostly) following a tutorial everydayrails.com trying to write a test that shows that my user model requires an email:

 17   it "requires an email" do
 18     user = FactoryGirl.create(:user, email: nil)
 19     expect( user ).to_not be_valid
 20   end

But this fails... because my user model requires an email?

Failures:

  1) User requires an email
     Failure/Error: user = FactoryGirl.create(:user, email: nil)

     ActiveRecord::RecordInvalid:
       Validation failed: Email can't be blank
     # ./spec/models/user_spec.rb:18:in `block (2 levels) in <top (required)>'

What am I doing wrong here?