Thorougly testing regex validations

regex_validations.rb

# /app/models/foo.rb
class Foo < ActiveRecord::Base
  validates_format_of :zip, with: /^[0-9]{5}$/, message: 'must be a valid 5-digit ZIP'
end

# /spec/models/foo_spec.rb
require 'spec_helper'
describe Foo do
  describe 'validations' do
    it { should_not allow_value("12345\n12345").for(:zip) }
  end 
end

# What do you think happens???

# output: `$ rspec spec/models/foo_spec.rb`
F
Expected errors when zip is set to "12345\n12345", got no errors

# Why?

# /app/models/foo.rb corrected
class Foo < ActiveRecord::Base
  validates_format_of :zip, with: /\A[0-9]{5}\z/, message: 'must be a valid 5-digit ZIP'
end

# Use `\A` (beginning of string) and `\z` (end of string) where possible in stead of `^` and `$`.