feat: log a warning when too many interactions are set on the mock service at once

Author: bethesque

lib/pact/mock_service/app.rb

@@ -15,12 +15,12 @@ def self.new *args
     end
 
     class App
-
       def initialize options = {}
         logger = Logger.from_options(options)
+        stubbing = options[:stub_pactfile_paths] && options[:stub_pactfile_paths].any?
         @name = options.fetch(:name, "MockService")
-        @session = Session.new(options.merge(logger: logger))
-        setup_stub(options[:stub_pactfile_paths]) if options[:stub_pactfile_paths]
+        @session = Session.new(options.merge(logger: logger, warn_on_too_many_interactions: !stubbing))
+        setup_stub(options[:stub_pactfile_paths]) if stubbing
         request_handlers = RequestHandlers.new(@name, logger, @session, options)
         @app = Rack::Builder.app do
           use Pact::Consumer::MockService::ErrorHandler, logger

lib/pact/mock_service/session.rb

@@ -17,6 +17,8 @@ def initialize options
         @expected_interactions = Interactions::ExpectedInteractions.new
         @actual_interactions = Interactions::ActualInteractions.new
         @verified_interactions = Interactions::VerifiedInteractions.new
+        @warn_on_too_many_interactions = options[:warn_on_too_many_interactions] || false
+        @max_concurrent_interactions_before_warning = get_max_concurrent_interactions_before_warning
         @consumer_contract_details = {
           pact_dir: options[:pact_dir],
           consumer: {name: options[:consumer]},
@@ -64,10 +66,15 @@ def add_expected_interaction interaction
 
       private
 
+      attr_reader :warn_on_too_many_interactions, :max_concurrent_interactions_before_warning
+
       def really_add_expected_interaction interaction
         expected_interactions << interaction
         logger.info "Registered expected interaction #{interaction.request.method_and_path}"
         logger.debug JSON.pretty_generate InteractionDecorator.new(interaction)
+        if warn_on_too_many_interactions && expected_interactions.size > max_concurrent_interactions_before_warning
+          logger.warn "You currently have #{expected_interactions.size} interactions mocked at the same time. This suggests the scope of your consumer tests is larger than recommended, and you may find them hard to debug and maintain. See https://pact.io/too-many-interactions for more information."
+        end
       end
 
       def handle_almost_duplicate_interaction previous_interaction, interaction
@@ -81,6 +88,9 @@ def interaction_already_verified_with_same_description_and_provider_state_but_no
         other && other != interaction ? other : nil
       end
 
+      def get_max_concurrent_interactions_before_warning
+        ENV['PACT_MAX_CONCURRENT_INTERACTIONS_BEFORE_WARNING'] ? ENV['PACT_MAX_CONCURRENT_INTERACTIONS_BEFORE_WARNING'].to_i : 3
+      end
     end
   end
 end

spec/lib/pact/mock_service/session_spec.rb

@@ -7,7 +7,6 @@ module Pact::MockService
     let(:logger) { double('Logger').as_null_object }
 
     describe "set_expected_interactions" do
-
       let(:interaction_1) { InteractionFactory.create }
       let(:interaction_2) { InteractionFactory.create }
       let(:interactions) { [interaction_1, interaction_2] }
@@ -84,6 +83,7 @@ module Pact::MockService
       let(:expected_interactions) { instance_double('Interactions::ExpectedInteractions', :<< => nil) }
       let(:actual_interactions) { instance_double('Interactions::ActualInteractions') }
       let(:verified_interactions) { instance_double('Interactions::VerifiedInteractions') }
+      let(:matching_interaction) { nil }
 
       before do
         allow(Interactions::ExpectedInteractions).to receive(:new).and_return(expected_interactions)
@@ -95,8 +95,6 @@ module Pact::MockService
       subject { Session.new(logger: logger) }
 
       context "when there is no already verified interaction with the same description and provider state" do
-        let(:matching_interaction) { nil }
-
         it "adds the new interaction to the interaction list" do
           expect(expected_interactions).to receive(:<<).with(interaction_1)
           subject.add_expected_interaction interaction_1
@@ -138,6 +136,31 @@ module Pact::MockService
           expect { subject.add_expected_interaction interaction_1 }.to raise_error SameSameButDifferentError, diff_message
         end
       end
+
+      context "when there are more than 3 interactions mocked at the same time" do
+        subject { Session.new(logger: logger, warn_on_too_many_interactions: true) }
+
+        it "logs a warning" do
+          allow(expected_interactions).to receive(:size).and_return(3, 4)
+          expect(logger).to receive(:warn).with(/You currently have 4 interactions/).once
+          subject.add_expected_interaction(InteractionFactory.create('description' => 'third interaction')) # no warning
+          subject.add_expected_interaction(InteractionFactory.create('description' => 'forth interaction')) # warning
+        end
+
+        context "when PACT_MAX_CONCURRENT_INTERACTIONS_BEFORE_WARNING is set" do
+          before do
+            allow(ENV).to receive(:[]).and_call_original
+            allow(ENV).to receive(:[]).with("PACT_MAX_CONCURRENT_INTERACTIONS_BEFORE_WARNING").and_return("5")
+          end
+
+          it "logs a warning when over the configured limit" do
+            allow(expected_interactions).to receive(:size).and_return(5, 6)
+            expect(logger).to receive(:warn).with(/You currently have 6 interactions/).once
+            subject.add_expected_interaction(InteractionFactory.create('description' => 'fifth interaction')) # no warning
+            subject.add_expected_interaction(InteractionFactory.create('description' => 'sixth interaction')) # warning
+          end
+        end
+      end
     end
   end
 end