Writing An API Client With Test, Staging, And Production In Mind

I was recently tasked with this story:

Background:
  Given I go to the sign up page
  And I fill in "Email" with "new@example.com"
  And I fill in "Password" with "password"

Scenario: Visitor signs up and does not want email
  When I press "Sign up"
  Then email service is not notified "new@example.com" signed up

Scenario: Visitor signs up and wants email
  When I check "Please email me"
  And I press "Sign up"
  Then email service is notified "new@example.com" signed up

The email service in question was internal, accessible via an HTTP API, and did not have a Ruby client library.

So, I had to write and test my own. The usual approach would involve using a HTTP stubbing library like Sham Rack or Artifice. I decided to try something different and see how it felt.

First, I needed an interface that I could test:

Then /^email service is notified "([^"]*)" signed up$/ do |email|
  EmailService.notifications.should include(email)
end

Then /^email service is not notified "([^"]*)" signed up$/ do |email|
  EmailService.notifications.should_not include(email)
end

I’m re-using a pattern (“store data in a simple array for easy state-based testing”) we’ve used before for Javascript integration testing Mixpanel.

So I have the start to an EmailService interface. I thought I wanted it invoked as part of an after_save callback on the User model, so here’s that spec:

describe User, 'who opts into email' do
  subject { build(:user, email_opt_in: true) }

  before do
    EmailService.stubs(:notify)
    subject.save
  end

  it 'notifies EmailService' do
    EmailService.should have_received(:notify).with(subject.email)
  end
end

describe User, 'who does not opt into email' do
  subject { build(:user, email_opt_in: false) }

  before do
    EmailService.stubs(:notify)
    subject.save
  end

  it 'does not notify EmailService' do
    EmailService.should have_received(:notify).never
  end
end

This is the stubbing and spying technique and uses RSpec, mocha, and bourne.

My thought process was that I needed an active verb, notify to invoke when the user is created, but that will store the invocation in a notifications array that the Cucumber step definition needs to check state (I don’t want to stub, spy, or mock in an integration test).

So, making the user spec pass isn’t bad:

require 'email_service/notifier'

class User < ActiveRecord::Base
  after_create do
    if email_opt_in?
      EmailService.notify(email)
    end
  end
end

Now, the EmailService can be spec'ed. We already had John Nunemaker’s HTTParty as a dependency in the app, and I only had to make one HTTP POST, so I knew I would be re-using HTTParty’s interface.

describe EmailService::Notifier, '#post' do
  subject { EmailService::Notifier }

  let(:email) { 'new-signup@example.com' }

  before do
    subject.stubs(:post)
    subject.new(email).post
  end

  it 'POSTs to email service with API_KEY and given email' do
    subject.should have_received(:post).with(
      subject::URL, query: { api_key: subject::PARAMS, email: email }
    )
  end
end

What I care about here is that during the one POST the app has to make, that the parameters are correct. This is close to hitting the live service as I’m willing to get without making an HTTP request.

I had an internal debate with myself while writing it over whether this is “stubbing the system under test” (considered bad practice). I decided “no” because despite the subject being stubbed, the system under test is actually the EmailService::Notifier#post method.

The stubbed and spied method is also mixed in from HTTParty, so I feel clean with this approach.

Making it pass:

require 'httparty'

module EmailService
  class << self
    attr_accessor :notifications
  end

  def self.notify(email, live = false)
    if Rails.env.production? || live
      Notifier.new(email).post
    else
      self.notifications << email
    end
  end

  class Notifier
    include HTTParty

    API_KEY = 12345
    URL = 'http://emailservice.example.com'

    def initialize(email)
      @url   = URL
      @email = email
    end

    def post
      self.class.post(@url, query: { api_key: API_KEY, email: @email })
    end
  end
end

Summary

• I’ve got an environment-specific conditional inside the true public interface for the service, EmailService.notify, which is used by the User model.
• In my integration test and in the development environment, all that happens is an array is populated, which makes it easy to confirm that it was notified correctly.
• I’ve got a unit test that makes sure the correct URL and API key are used.
• I’ve got a way to override EmailService.notify with the live flag so I can invoke it from the Rails console on production or staging when testing or debugging.

This almost takes longer to describe than to code but I’m curious what people think about this style of writing an API client with test, staging, and production environments in mind. How do you do things differently?