don't touch the response object until after we call `get`

actionpack/test/controller/live_stream_test.rb

@@ -281,10 +281,9 @@ def test_async_stream
       @controller.latch = Concurrent::CountDownLatch.new
       parts             = ['hello', 'world']
 
-      @controller.request  = @request
-      @controller.response = @response
+      get :blocking_stream
 
-      t = Thread.new(@response) { |resp|
+      t = Thread.new(response) { |resp|
         resp.await_commit
         resp.stream.each do |part|
           assert_equal parts.shift, part
@@ -294,8 +293,6 @@ def test_async_stream
         end
       }
 
-      @controller.process :blocking_stream
-
       assert t.join(3), 'timeout expired before the thread terminated'
     end