Workaround for: ThreadError: already initialized with Ruby 2.6.0

spec/spec_helper.rb

@@ -39,3 +39,20 @@
   #     --seed 1234
   config.order = "random"
 end
+
+# Workaround for ThreadError: already initialized with Ruby 2.6.0
+# See https://github.com/rails/rails/issues/34790
+if RUBY_VERSION >= '2.6.0'
+  if Rails.version < '5'
+    class ActionController::TestResponse < ActionDispatch::TestResponse
+      def recycle!
+        # hack to avoid MonitorMixin double-initialize error:
+        @mon_mutex_owner_object_id = nil
+        @mon_mutex = nil
+        initialize
+      end
+    end
+  else
+    puts "Monkeypatch for ActionController::TestResponse no longer needed"
+  end
+end