Best practice: Ruby/Rails Rspec regex testing

Could you tell me how to test regex-code correctly?

I test my user-login attribute with following code:

# user.rb
class User < ActiveRecord::Base
  #...
  validates_format_of :login开发者_运维技巧, :with => /^[a-zA-z0-9_.]{3,18}$/
end

# user_spec.rb
describe User do
  before(:each) do 
    @user = Factory.build(:user)
    @user.save
  end

  subject { @user }
  it { should be_valid }

  it { should_not allow_value("b lah").for(:login) }
  it { should_not allow_value("bälah").for(:login) }
  it { should_not allow_value("b@lah").for(:login) }
  it { should_not allow_value("bülah").for(:login) }
  it { should_not allow_value("bßlah").for(:login) }
  it { should_not allow_value("b!lah").for(:login) }
  it { should_not allow_value("b%lah").for(:login) }
  it { should_not allow_value("b)lah").for(:login) }
  # ....
  # Shall I test here every special sign????
end

But it seems very redundant and not secure.... Is there a best practice? Thx!

---

You're not really testing your model here, you're testing your regex. It's not quite the same thing. Also, you're testing the same aspect of your regex, that it only allows [a-zA-z0-9_.], again and again. If you want to apply different tests, test different aspects of it, eg with "lo" (<3 chars) or "12345678901234567890" (>18 chars).

Also, if you wanted to dry it up you could do something like

invalid_logins = ["b lah","bälah","b@lah","bülah","bßlah","b!lah","b%lah","b)lah"]
invalid_logins.each do |s|
  it { should_not allow_value(s).for(:login) }
end