Currently test `#test_logger_does_not_mutate_app_return` doesn't
test mutation of response and the test passes with and without changes
added in #32444. `#freeze` response in the test in order to
test mutation.
If @app.call returns an object that is saved (for e.g., in a constant), the mutation results in a continuing cycle of wrapping the body in Rack::BodyProxy, eventually leading to SystemStackError
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
On branch fix-return-response-mutation-rack-logger - Tue 3 Apr 2018 19:54:28 PDT by Geoff Lee <geoff.lee@lendesk.com>
