Validate uniqueness of user email address

* Make user.email attribute unique
* Render validations error messages in users/new view

app/models/user.rb

@@ -8,7 +8,10 @@ class User < ActiveRecord::Base
 
   has_many :playlists
 
-  validates_presence_of :email, :password_hash
+  validates :email,
+    :presence => true,
+    :uniqueness => true
+  validates_presence_of :password_hash
   validates_confirmation_of :password
 
   def password=(plain_password)

app/views/users/new.html.haml

@@ -1,4 +1,8 @@
 = form_for(@user, :url => users_path) do |f|
+  - if @user.errors.any?
+    %ul
+      - @user.errors.full_messages.each do |m|
+        %li= m
   %table
     %tbody
       %tr

features/step_definitions/user_step.rb

@@ -0,0 +1,12 @@
+Given /^a user with "([^"]*)" email address exists$/ do |email|
+  Factory.create(:user, :email => email)
+end
+
+When /^I register with "([^"]*)" email address$/ do |email|
+  visit new_user_path
+  user = Factory.build(:user)
+  fill_in('Email', :with => email)
+  fill_in('Password', :with => user.password)
+  fill_in('Password confirmation', :with => user.password)
+  click_button('Sign up')
+end

features/user.feature

@@ -9,3 +9,8 @@ Feature: User
     When I follow the sign up link
     And I fill in the sign up form
     Then I should be redirected to the home page
+
+  Scenario: User can't register twice with the same email address
+    Given a user with "unique@example.net" email address exists
+    When I register with "unique@example.net" email address
+    Then I should see "Email has already been taken"

spec/models/user_spec.rb

@@ -32,6 +32,14 @@ describe User do
     it { should_not be_valid }
   end
 
+  context 'when a user with the same email address already exists' do
+    it 'should not be valid' do
+      user = Factory.create(:user, :email => 'unique@example.net')
+      new_user = Factory.build(:user, :email => user.email)
+      new_user.should_not be_valid
+    end
+  end
+
   describe '#password=' do
     it 'stores a bcrypt hash of the password in password_hash' do
       BCrypt::Password.new(user.password_hash).should == user.password

spec/views/users/new.html.haml_spec.rb

@@ -45,4 +45,15 @@ describe 'users/new.html.haml' do
       :text => 'Password confirmation'
     )
   end
+
+  context 'when the user has some validation errors' do
+    it 'on the email address uniqueness' do
+      user = Factory.create(:user, :email => 'unique@example.net')
+      new_user = Factory.build(:user, :email => user.email)
+      new_user.save
+      assign :user, new_user
+      render
+      rendered.should have_content 'Email has already been taken'
+    end
+  end
 end