Fix authentication_generator_test

Those tests started to fail as soon as we started developing 8.1 since
it is not present on rubygems.

We should not have to generate a new app and install gems to be able to
test the behavior of this generator.

I used the same techniques we use in the application generator mocking
the commands that are executed and generating only the files that are
necessary to test the behavior of this generator.

Author: rafaelfranca

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

@@ -46,8 +46,8 @@ def enable_bcrypt
       end
 
       def add_migrations
-        generate "migration CreateUsers email_address:string!:uniq password_digest:string! --force"
-        generate "migration CreateSessions user:references ip_address:string user_agent:string --force"
+        generate "migration", "CreateUsers", "email_address:string!:uniq password_digest:string!", "--force"
+        generate "migration", "CreateSessions", "user:references ip_address:string user_agent:string", "--force"
       end
 
       hook_for :test_framework

railties/test/generators/authentication_generator_test.rb

@@ -8,21 +8,21 @@ class AuthenticationGeneratorTest < Rails::Generators::TestCase
   include GeneratorsTestHelper
 
   def setup
-    Rails.application = TestApp::Application
-    Rails.application.config.root = Pathname(destination_root)
+    FileUtils.mkdir_p("#{destination_root}/app/controllers")
+    File.write("#{destination_root}/app/controllers/application_controller.rb", <<~RUBY)
+      class ApplicationController < ActionController::Base
+      end
+    RUBY
 
-    self.class.tests Rails::Generators::AppGenerator
-    run_generator([destination_root, "--no-skip-bundle"])
+    copy_gemfile
 
-    self.class.tests Rails::Generators::AuthenticationGenerator
-  end
-
-  def teardown
-    Rails.application = Rails.application.instance
+    copy_routes
   end
 
   def test_authentication_generator
-    run_generator
+    generator([destination_root])
+
+    run_generator_instance
 
     assert_file "app/models/user.rb"
     assert_file "app/models/current.rb"
@@ -46,30 +46,27 @@ def test_authentication_generator
       assert_match(/resource :session/, content)
     end
 
-    assert_migration "db/migrate/create_sessions.rb" do |content|
-      assert_match(/t.references :user, null: false, foreign_key: true/, content)
-    end
-
-    assert_migration "db/migrate/create_users.rb" do |content|
-      assert_match(/t.string :password_digest, null: false/, content)
-    end
+    assert_includes @rails_commands, "generate migration CreateUsers email_address:string!:uniq password_digest:string! --force"
+    assert_includes @rails_commands, "generate migration CreateSessions user:references ip_address:string user_agent:string --force"
 
     assert_file "test/models/user_test.rb"
     assert_file "test/fixtures/users.yml"
   end
 
   def test_authentication_generator_without_bcrypt_in_gemfile
-    File.write("Gemfile", File.read("Gemfile").sub(/# gem "bcrypt".*\n/, ""))
+    File.write("#{destination_root}/Gemfile", File.read("#{destination_root}/Gemfile").sub(/# gem "bcrypt".*\n/, ""))
 
-    run_generator
+    generator([destination_root])
 
-    assert_file "Gemfile" do |content|
-      assert_match(/\ngem "bcrypt"/, content)
-    end
+    run_generator_instance
+
+    assert_includes @bundle_commands, [:bundle, "add bcrypt", { capture: true }]
   end
 
   def test_authentication_generator_with_api_flag
-    run_generator(["--api"])
+    generator([destination_root], api: true)
+
+    run_generator_instance
 
     assert_file "app/models/user.rb"
     assert_file "app/models/current.rb"
@@ -93,21 +90,40 @@ def test_authentication_generator_with_api_flag
       assert_match(/resource :session/, content)
     end
 
-    assert_migration "db/migrate/create_sessions.rb" do |content|
-      assert_match(/t.references :user, null: false, foreign_key: true/, content)
-    end
-
-    assert_migration "db/migrate/create_users.rb" do |content|
-      assert_match(/t.string :password_digest, null: false/, content)
-    end
+    assert_includes @rails_commands, "generate migration CreateUsers email_address:string!:uniq password_digest:string! --force"
+    assert_includes @rails_commands, "generate migration CreateSessions user:references ip_address:string user_agent:string --force"
 
     assert_file "test/models/user_test.rb"
     assert_file "test/fixtures/users.yml"
   end
 
   def test_model_test_is_skipped_if_test_framework_is_given
-    content = run_generator ["authentication", "-t", "rspec"]
+    generator([destination_root], ["-t", "rspec"])
+
+    content = run_generator_instance
+
     assert_match(/rspec \[not found\]/, content)
     assert_no_file "test/models/user_test.rb"
   end
+
+  private
+
+  def run_generator_instance
+    commands = []
+    command_stub ||= -> (command, *args) { commands << [command, *args] }
+
+    @rails_commands = []
+    @rails_command_stub ||= -> (command, *_) { @rails_commands << command }
+
+    content = nil
+    generator.stub(:execute_command, command_stub) do
+      generator.stub(:rails_command, @rails_command_stub) do
+        content = super
+      end
+    end
+
+    @bundle_commands = commands.filter { |command, _| command == :bundle }
+
+    content
+  end
 end