1 files changed, 20 insertions, 2 deletions
diff --git a/railties/test/rack_logger_test.rb b/railties/test/rack_logger_test.rb
index e47f30d5b6..6e8f333e1d 100644
--- a/railties/test/rack_logger_test.rb
+++ b/railties/test/rack_logger_test.rb
@@ -14,14 +14,21 @@ module Rails
 
         attr_reader :logger
 
-        def initialize(logger = NULL, taggers = nil, &block)
-          super(->(_) { block.call; [200, {}, []] }, taggers)
+        def initialize(logger = NULL, app: nil, taggers: nil, &block)
+          app ||= ->(_) { block.call; [200, {}, []] }
+          super(app, taggers)
           @logger = logger
         end
 
         def development?; false; end
       end
 
+      class TestApp < Struct.new(:response)
+        def call(_env)
+          response
+        end
+      end
+
       Subscriber = Struct.new(:starts, :finishes) do
         def initialize(starts = [], finishes = [])
           super
@@ -72,6 +79,17 @@ module Rails
           end
         end
       end
+
+      def test_logger_does_not_mutate_app_return
+        response = [].freeze
+        app = TestApp.new(response)
+        logger = TestLogger.new(app: app)
+        assert_no_changes("response") do
+          assert_nothing_raised do
+            logger.call("REQUEST_METHOD" => "GET")
+          end
+        end
+      end
     end
   end
 end