Following code has been tested with rails 2.2.2 .

shoulda is a great testing tool. If you have a validation for the presence of a field then testing it is as easy as this.

class User < ActiveRecord::Base
  validates_presence_of :email
end

class UserTest < ActiveSupport::TestCase
  should_validate_presence_of :email
end

For one line of code, one line of testing. This is awesome.

However when it comes to email, not only I need to make sure it is present, I need to validate the format of it.

validates_format_of :email, :with => /(\A(\s*)\Z)|(\A([^@\s]+)@((?:[-a-z0-9]+\.)+[a-z]{2,})\Z)/i

I thought shoulda will have something like should_validate_format_of/. But shoulda does not provide anything like that. No problem it is easy to create something like that. The code is here and it can be put at config/initializer/should_validate_format_of.rb.

With that code in testing for format validation is as simple as

should_validate_format_of :email, 
                          :invalid_value => 'foo'

should_validate_format_of :email, 
                          :message => /Email must be a valid email address/,
                          :invalid_value => 'foo'

Above two cases are illustrated. The first is one with the default message and the second one is a custom message. You should pass an invalid value which is NOT matching the regular expression.

Happy testing.