CI: Lock down Rack for old Grape v1.x versions

test/multiverse/suites/grape/Envfile

@@ -19,9 +19,15 @@ def activesupport_version(grape_version)
   ", '< 7.1'" if grape_version&.include?('1.5')
 end
 
+# Grape v1.x expects Rack to deliver `rack/auth/digest/md5`, but Rack
+# stopped offering that class in Rack v3.1.0
+def rack_version(grape_version)
+  ", '~> 3.0.11'" if grape_version.to_s.sub(/^[^\d]+/, '').start_with?('1.')
+end
+
 def gem_list(grape_version = nil)
   <<~RB
-    gem 'rack'
+    gem 'rack'#{rack_version(grape_version)}
     gem 'rack-test', '>= 0.8.0'
     gem 'grape'#{grape_version}
 

test/multiverse/suites/grape/grape_test.rb

@@ -220,16 +220,23 @@ def test_request_and_response_attributes_recorded_as_agent_attributes
         'request.headers.host' => last_request.host,
         'request.method' => last_request.request_method
       }
+      actual = agent_attributes_for_single_event_posted_without_ignored_attributes
 
       # Rack >= 2.1 changes how/when contentLength is computed and Grape >= 1.3 also changes to deal with this.
       # interactions with Rack < 2.1 and >= 2.1 differ on response.headers.contentLength calculations
       # so we remove it when it is zero since its not present in such cases.
+      #
+      # Rack >= 3.1 further changes things, so we also excuse an actual 0 value
+      # when it is in play
       if Gem::Version.new(::Grape::VERSION) >= Gem::Version.new('1.3.0')
-        if expected['response.headers.contentLength'] == 0
+        rack31_plus_and_zero = Rack.respond_to?(:release) &&
+          Gem::Version.new(Rack.release) >= Gem::Version.new('3.1.0') &&
+          actual['request.headers.contentLength'] == 0
+
+        if expected['response.headers.contentLength'] == 0 || rack31_plus_and_zero
           expected.delete('response.headers.contentLength')
         end
       end
-      actual = agent_attributes_for_single_event_posted_without_ignored_attributes
 
       assert_equal(expected, actual)
     end