Add login_as(user) testing helper when generating authentication (rails#53708)

* Add a `SessionTestHelper` module with `sign_in_as(user)` and `sign_out` test helpers when
running `rails g authentication`. Simplifies authentication in integration tests.

* Style

---------

Co-authored-by: David Heinemeier Hansson <[email protected]>

Author: gobijan

railties/CHANGELOG.md

@@ -1,3 +1,8 @@
+*   Add a `SessionTestHelper` module with `sign_in_as(user)` and `sign_out` test helpers when
+    running `rails g authentication`. Simplifies authentication in integration tests.
+
+    *Bijan Rahnema*
+
 *   Rate limit password resets in authentication generator
 
     This helps mitigate abuse from attackers spamming the password reset form.

railties/lib/rails/generators/rails/authentication/authentication_generator.rb

@@ -27,6 +27,7 @@ def create_authentication_files
         template "app/views/passwords_mailer/reset.text.erb"
 
         template "test/mailers/previews/passwords_mailer_preview.rb"
+        template "test/helpers/session_test_helper.rb"
       end
 
       def configure_application_controller
@@ -52,6 +53,11 @@ def add_migrations
         generate "migration", "CreateSessions", "user:references ip_address:string user_agent:string", "--force"
       end
 
+      def configure_test_helper
+        inject_into_file "test/test_helper.rb", "require_relative \"helpers/session_test_helper\"\n", after: "require \"rails/test_help\"\n"
+        inject_into_class "test/test_helper.rb", "TestCase", "    include SessionTestHelper\n"
+      end
+
       hook_for :test_framework
     end
   end

railties/lib/rails/generators/rails/authentication/templates/test/helpers/session_test_helper.rb.tt

@@ -0,0 +1,15 @@
+module SessionTestHelper
+  def sign_in_as(user)
+    Current.session = user.sessions.create!
+
+    ActionDispatch::TestRequest.create.cookie_jar.tap do |cookie_jar|
+      cookie_jar.signed[:session_id] = Current.session.id
+      cookies[:session_id] = cookie_jar[:session_id]
+    end
+  end
+
+  def sign_out
+    Current.session&.destroy!
+    cookies.delete(:session_id)
+  end
+end

railties/test/generators/authentication_generator_test.rb

@@ -13,6 +13,14 @@ def setup
       class ApplicationController < ActionController::Base
       end
     RUBY
+    FileUtils.mkdir_p("#{destination_root}/test")
+    File.write("#{destination_root}/test/test_helper.rb", <<~RUBY)
+      require "rails/test_help"
+      module ActiveSupport
+        class TestCase
+        end
+      end
+    RUBY
 
     copy_gemfile
 
@@ -52,6 +60,11 @@ def test_authentication_generator
 
     assert_file "test/models/user_test.rb"
     assert_file "test/fixtures/users.yml"
+
+    assert_file "test/test_helper.rb" do |content|
+      assert_match(/session_test_helper/, content)
+      assert_match(/SessionTestHelper/, content)
+    end
   end
 
   def test_authentication_generator_without_bcrypt_in_gemfile
@@ -96,6 +109,11 @@ def test_authentication_generator_with_api_flag
 
     assert_file "test/models/user_test.rb"
     assert_file "test/fixtures/users.yml"
+
+    assert_file "test/test_helper.rb" do |content|
+      assert_match(/session_test_helper/, content)
+      assert_match(/SessionTestHelper/, content)
+    end
   end
 
   def test_model_test_is_skipped_if_test_framework_is_given