Correctly handle unknown object in parallel tests

DRb wraps in `DRbUnknown` if the data contains a type that can not be
resolved locally. This can happen if an error occurs in the test and the
error class can not be resolved on the server side.

When this happens, an instance of `DRbUnknown` is passed to the `result`
of `Server#record`. This causes another error(undefined method assertions
for #<DRb::DRbUnknown:> (NoMethodError)) in `reporter.record`.
This can confirm by the following steps.

```
$ rails new app -B --dev; cd app
$ rails g scaffold user name:string
$ edit `config.action_controller.allow_forgery_protection = true` in environments/test.rb
$ bin/rails t
```

In the case of `DRbUnknown` occurs, can't resolve error exception. So wrap
exception with `DRbRemoteError` in the same way as an unmarshalled object.

2 files changed, 16 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/testing/parallelization.rb b/activesupport/lib/active_support/testing/parallelization.rb
index 9c8dffa9d8..24c4f18931 100644
--- a/activesupport/lib/active_support/testing/parallelization.rb
+++ b/activesupport/lib/active_support/testing/parallelization.rb
@@ -15,6 +15,8 @@ module ActiveSupport
         end
 
         def record(reporter, result)
+          raise DRb::DRbConnError if result.is_a?(DRb::DRbUnknown)
+
           reporter.synchronize do
             reporter.record(result)
           end
diff --git a/railties/test/application/test_runner_test.rb b/railties/test/application/test_runner_test.rb
index 0d7645e794..140703e118 100644
--- a/railties/test/application/test_runner_test.rb
+++ b/railties/test/application/test_runner_test.rb
@@ -586,6 +586,20 @@ module ApplicationTests
       assert_match "1 runs, 0 assertions, 0 failures, 1 errors", output
     end
 
+    def test_run_in_parallel_with_unknown_object
+      create_scaffold
+      app_file "config/environments/test.rb", <<-RUBY
+        Rails.application.configure do
+          config.action_controller.allow_forgery_protection = true
+          config.action_dispatch.show_exceptions = false
+        end
+      RUBY
+
+      output = run_test_command("-n test_should_create_user")
+
+      assert_match "ActionController::InvalidAuthenticityToken", output
+    end
+
     def test_raise_error_when_specified_file_does_not_exist
       error = capture(:stderr) { run_test_command("test/not_exists.rb", stderr: true) }
       assert_match(%r{cannot load such file.+test/not_exists\.rb}, error)