Add specific integration test for ActionDispatch::TestResponse

Author: jas14

spec/support/shared_examples/action_dispatch.rb

@@ -1,4 +1,49 @@
 # frozen_string_literal: true
 
 shared_examples_for 'integration with ActionDispatch' do
+  context 'when testing attributes of an ActionDispatch::TestResponse' do
+    it 'produces the correct failure message when used in the positive' do
+      as_both_colored_and_uncolored do |color_enabled|
+        snippet = <<~RUBY
+          request = ActionDispatch::TestRequest.create
+          response = ActionDispatch::TestResponse.new(200, {}, []).tap do |response|
+            response.request = request
+          end
+
+          # The other attributes of TestResponse differ across Rails versions. We don't care about them
+          # for the purposes of this test.
+          ActionDispatch::TestResponse.define_method(:attributes_for_super_diff) { {request: request} }
+
+          expect(response).to be_bad_request
+        RUBY
+        program =
+          make_rspec_action_dispatch_program(snippet, color_enabled: color_enabled)
+
+        expected_output =
+          build_expected_output(
+            color_enabled: color_enabled,
+            snippet: 'expect(response).to be_bad_request',
+            newline_before_expectation: true,
+            expectation:
+              proc do
+                line do
+                  plain '                     Expected '
+                  actual '#<ActionDispatch::TestResponse request: #<ActionDispatch::TestRequest GET "http://test.host/" for 0.0.0.0>>'
+                end
+
+                line do
+                  plain 'to return a truthy result for '
+                  expected 'bad_request?'
+                  plain ' or '
+                  expected 'bad_requests?'
+                end
+              end
+          )
+
+        expect(program).to produce_output_when_run(expected_output).in_color(
+          color_enabled
+        )
+      end
+    end
+  end
 end