Idea for FixturePact

1.md

Pact is great for HTTP microservices that communicate directly with each other, but many services use an intermediate system that acts as a pipe (eg. a queue, S3 bucket). The agreement about the format of the message is really between the two ends of the chain, not between the links immediatly adjacent.

The pact concept should be able to be applied to non-http services. The code below is an attempt to come up with a DSL for a new pact library that uses the same pact matching concepts, but does not constrain the communication protocol.

Thoughts/improvements appreciated, but remember Gists do not send notifications when you post a comment :|

consumer.rb

require 'fixture_pact/consumer'

FixturePact.consumer "Billing Run" do
   
   has_fixture_pact_with "Billable Purchases" do
      pact_builder :billable_purchases
   end
      
end

# Repository wrapping S3 bucket

class BillablePurchasesRepository
   
   def self.purchases
      JSON.parse(S3.some_object).collect do | purchase_hash |
         Purchase.new(purchase_hash)
      end
   end
   
end

# Spec for repository

describe BillablePurchasesRepository do
   
   let(:billable_purchases_list) { 
      billable_purchases
         .given("a customer has purchased an online product")
         .will_provide("a list of billable purchases")
         .with([{amount: 12, date: Pact::Term.new(matcher: /\d\d\/\d\d\/\d\d/, generate: '12/12/12'}])
      }
   before do
      allow(S3).to receive(:some_object).and_return(billable_purchases_list.to_json)   
   end
   
   it "returns a list of Purchases" do
      expect(BillablePurchasesRepository.purchases.size).to eq 1
      expect(BillablePurchasesRepository.purchases.first).to be_instance_of(Purchase)
   end
   
end

provider.rb

require 'fixture_pact/provider'

FixturePact.provider "Billable Purchases" do
   
   honours_fixture_pact_with "Billing Run" do
      fixture_pact_url "http://blah/blah"
   end
   
end

FixturePact.provider_states_for "Billing Run" do
   
   provider_state "a customer has purchased an online product" do
      set_up do
         # insert a purchase into something
      end
   end
   
end

FixturePact.to_verify "a list of billable purchases" do
   BillablePurchases.extract_purchases
end

Conceptually, this is harder to follow than the original pact. The fact that you need to create the fixture, then use it to stub something in a two stage process is a bit conceptually inelegant.

Is there any benefit to using this over JSON schema?