Failsafe exception returns text/plain.

It's best to just return text/plain when something has gone terribly
wrong.

Fixes #5660.

1 files changed, 16 insertions, 0 deletions

diff --git a/actionpack/test/controller/show_exceptions_test.rb b/actionpack/test/controller/show_exceptions_test.rb
index 351b9c4cfa..ab1bd0e3b6 100644
--- a/actionpack/test/controller/show_exceptions_test.rb
+++ b/actionpack/test/controller/show_exceptions_test.rb
@@ -93,4 +93,20 @@ module ShowExceptions
       assert_equal 'text/html', response.content_type.to_s
     end
   end
+
+  class ShowFailsafeExceptionsTest < ActionDispatch::IntegrationTest
+    def test_render_failsafe_exception
+      @app = ShowExceptionsOverridenController.action(:boom)
+      @exceptions_app = @app.instance_variable_get(:@exceptions_app)
+      @app.instance_variable_set(:@exceptions_app, nil)
+      $stderr = StringIO.new
+
+      get '/', {}, 'HTTP_ACCEPT' => 'text/json'
+      assert_response :internal_server_error
+      assert_equal 'text/plain', response.content_type.to_s
+
+      @app.instance_variable_set(:@exceptions_app, @exceptions_app)
+      $stderr = STDERR
+    end
+  end
 end