chore: add demo of message example without kafka

Author: YOU54F

.github/workflows/test.yml

@@ -35,6 +35,8 @@ jobs:
         working-directory: example/animal-service
       - name: Test Pact-Ruby v2 Specs
         run: "bundle exec rake spec:v2"
+      - name: Test Pact-Ruby v2 pact:specs
+        run: "bundle exec rake pact:v2:spec"
       - name: Test Pact-Ruby v2 Zoo App Specs
         run: "bundle install && bundle exec rake spec:v2"
         if: matrix.ruby_version > '3.0'

spec/internal/app/consumers/test_message_consumer.rb

@@ -0,0 +1,9 @@
+class TestMessageConsumer
+
+  def consume_message(message)
+    puts "Message consumed"
+    puts message.to_json
+    message
+  end
+  
+  end

spec/internal/app/producers/test_message_producer.rb

@@ -0,0 +1,12 @@
+class TestMessageProducer
+
+def publish_message()
+  message = {
+    "email": "jane@example.com",
+    "title": "Miss",
+    "first_name": "Jane",
+    "surname": "Doe"   
+  }
+end
+
+end

spec/pact/consumers/message_spec.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'pact/v2'
+require 'pact/v2/rspec'
+require_relative '../../internal/app/producers/test_message_producer'
+
+RSpec.describe 'Test Message Provider', :pact_v2 do
+  message_pact_provider 'Test Message Producer', opts: {
+    pact_dir: File.expand_path('../../pacts', __dir__),
+  }
+
+  handle_message 'a customer created message' do |provider_state|
+    body = TestMessageProducer.new.publish_message
+    metadata = {}
+    [body, metadata]
+  end
+end

spec/pact/providers/pact-ruby-v2-test-app/message_spec.rb

@@ -0,0 +1,65 @@
+require 'pact/v2'
+require 'pact/v2/rspec'
+require_relative '../../../internal/app/consumers/test_message_consumer'
+
+describe TestMessageConsumer, :pact_v2 do
+  has_message_pact_between 'Test Message Consumer', 'Test Message Provider'
+
+  subject(:consumer) { TestMessageConsumer.new }
+
+  describe 'Test Message Consumer' do
+    # Notice that the expected message payload has fields which are different to that of the actual producer.
+    # The TestMessageProducer actually sends a message with an additional 'title' field and a renamed 'surname' field.
+    # See app/producers/test_message_producer.rb.
+
+    # before do
+    #   # Here we are calling test_message_producer, which is mocking the actual TestMessageProducer defined in app/producers/test_message_producer.rb.
+    #   # In pact-message we use mocked providers in consumer side tests. These are defined in a similar way to mocked APIs/service providers in standard HTTP CDCT.
+    #   # See spec/support/pact_spec_helper.rb.
+    #   let(:expected_payload)
+    #   {
+    #     "email": match_type_of('jane@example.com'),
+    #     "first_name": match_type_of('Jane')
+    #     # "last_name": Pact.like("Doe") # uncomment to see failure in provider code
+    #   }
+
+    #   let(:interaction) do
+    #     new_interaction.given('A customer is created')
+    #                          .upon_receiving('a customer created message')
+    #                          # .with_metadata()
+    #                          # .with_json_contents(match_type_of(expected_payload))
+    #                          .with_json_contents(expected_payload)
+    #   end
+    # end
+
+    # This test is a bit redundant, it's essentially marking our own homework and will always pass.
+    # However IRL the consumer would probably be doing something more complex which we could assert on.
+    # See spec/pacts/test_message_consumer-test_message_producer.json for the generated contract file.
+    # Note that this contract does not match what the producer outputs in app/producers/test_message_producer.rb..
+    # If we were to run producer side verification on this contract, it should fail.
+    # This failure would indicate a mismatch between the consumers expectations of the message format and what the producer actually sends.
+
+    let(:expected_payload) do
+      {
+        "email": match_type_of('jane@example.com'),
+        "first_name": match_type_of('Jane')
+        # "last_name": Pact.like("Doe") # uncomment to see failure in provider code
+      }
+    end
+
+    let(:interaction) do
+      new_interaction.given('A customer is created')
+                           .upon_receiving('a customer created message')
+                           # .with_metadata()
+                           # .with_json_contents(match_type_of(expected_payload))
+                           .with_json_contents(expected_payload)
+    end
+
+    it 'Successfully consumes the message and creates a pact contract file' do
+      interaction.execute do |json_payload, _meta|
+        @message = consumer.consume_message(json_payload)
+        expect(@message).to eq(json_payload)
+      end
+    end
+  end
+end