Invoke rails command inside the railties' test app with TestHelpers::Generation#rails

See #30520

railties/test/application/loading_test.rb

@@ -300,7 +300,7 @@ def change
       end
     MIGRATION
 
-    Dir.chdir(app_path) { `rake db:migrate` }
+    rails("db:migrate")
     require "#{rails_root}/config/environment"
 
     get "/title"
@@ -314,7 +314,7 @@ def change
       end
     MIGRATION
 
-    Dir.chdir(app_path) { `rake db:migrate` }
+    rails("db:migrate")
 
     get "/body"
     assert_equal "BODY", last_response.body

railties/test/application/rake_test.rb

@@ -101,6 +101,7 @@ def test_should_not_eager_load_model_for_rake
       add_to_config <<-RUBY
         rake_tasks do
           task do_nothing: :environment do
+            puts 'There is nothing'
           end
         end
       RUBY
@@ -113,10 +114,8 @@ def test_should_not_eager_load_model_for_rake
         raise 'should not be pre-required for rake even eager_load=true'
       RUBY
 
-      Dir.chdir(app_path) do
-        assert system("bin/rails do_nothing RAILS_ENV=production"),
-               "should not be pre-required for rake even eager_load=true"
-      end
+      output = rails("do_nothing", "RAILS_ENV=production")
+      assert_match "There is nothing", output
     end
 
     def test_code_statistics_sanity
@@ -294,9 +293,8 @@ def test_loading_only_yml_fixtures
 
     def test_scaffold_tests_pass_by_default
       rails "generate", "scaffold", "user", "username:string", "password:string"
-      output = Dir.chdir(app_path) do
-        `RAILS_ENV=test bin/rails db:migrate test`
-      end
+      with_rails_env("test") { rails("db:migrate") }
+      output = rails("test")
 
       assert_match(/7 runs, 9 assertions, 0 failures, 0 errors/, output)
       assert_no_match(/Errors running/, output)
@@ -313,9 +311,8 @@ class ApplicationController < ActionController::API
       RUBY
 
       rails "generate", "scaffold", "user", "username:string", "password:string"
-      output = Dir.chdir(app_path) do
-        `RAILS_ENV=test bin/rails db:migrate test`
-      end
+      with_rails_env("test") { rails("db:migrate") }
+      output = rails("test")
 
       assert_match(/5 runs, 7 assertions, 0 failures, 0 errors/, output)
       assert_no_match(/Errors running/, output)
@@ -325,9 +322,8 @@ def test_scaffold_with_references_columns_tests_pass_by_default
       rails "generate", "model", "Product"
       rails "generate", "model", "Cart"
       rails "generate", "scaffold", "LineItems", "product:references", "cart:belongs_to"
-      output = Dir.chdir(app_path) do
-        `RAILS_ENV=test bin/rails db:migrate test`
-      end
+      with_rails_env("test") { rails("db:migrate") }
+      output = rails("test")
 
       assert_match(/7 runs, 9 assertions, 0 failures, 0 errors/, output)
       assert_no_match(/Errors running/, output)

railties/test/application/server_test.rb

@@ -42,7 +42,7 @@ def teardown
         pid = Process.spawn("#{app_path}/bin/rails server -P tmp/dummy.pid", in: slave, out: slave, err: slave)
         assert_output("Listening", master)
 
-        Dir.chdir(app_path) { system("bin/rails restart") }
+        rails("restart")
 
         assert_output("Restarting", master)
         assert_output("Inherited", master)