Add test case to demonstrate Thread.current locals are cleared in the test environment

Co-authored-by: Ates Goral <[email protected]>

Author: spiderbites

actionpack/test/controller/live_stream_test.rb

@@ -658,6 +658,30 @@ def test_response_buffer_do_not_respond_to_to_ary
     end
   end
 
+  class LiveControllerThreadTest < ActionController::TestCase
+    class TestController < ActionController::Base
+      include ActionController::Live
+
+      def greet
+        response.headers["Content-Type"] = "text/event-stream"
+        %w{ hello world }.each do |word|
+          response.stream.write word
+        end
+        response.stream.close
+      end
+    end
+
+    tests TestController
+
+    def test_thread_locals_do_not_get_reset_in_test_environment
+      Thread.current[:setting]            = "aaron"
+
+      get :greet
+
+      assert_equal "aaron", Thread.current[:setting]
+    end
+  end
+
   class BufferTest < ActionController::TestCase
     def test_nil_callback
       buf = ActionController::Live::Buffer.new nil