The one where we DRY up Mongoid and Rspec using Shared Examples and Modules

The Situation: You’re adding Addresses to seemingly every document you have. Doctors, Patients, Insurance Agents. Even the Delivery Man – everybody has a contact.

The Problem: You’re tempted to copy/paste the field and validations, but your spidy-senses tell you not to.

Let’s DRY this up using modules and rspec shared examples. We’ll end up with a way you could enable fast rails tests on your Mongoid models.

tl;dr Shared examples describing a module. Include module in a mongoid class: The Gist.

Some Assumptions Before We Begin

You have a project setup with Mongoid (2.2+, Rspec 2.8+, and rspec-mongoid)
You are awesome

OK, so we would normally have a model for the Doctor like so:

class Doctor
    include Mongoid::Document
    include Mongoid::Timestamps

    field :first_name, type: String
    field :last_name, type: String
    field :phone_number, type: String
    field :address_line_1, type: String
    field :city, type: String
    field :state, type: String
    field :postal_code, type: string
    field :email, type :String
    validates_presence_of :last_name
    validates_presence_of :first_name
end

Step 1: Write those tests first

require 'spec_helper'

describe Doctor do
    it { should have_fields(:first_name, :last_name) }
    it { should have_fields(:phone_number, :email, :address_line_1, :city, :state, :postal_code) }
    it { should validate_presence_of(:first_name) }
    it { should validate_presence_of(:last_name) }
end

Note: If this doesn’t pass, you may need to add configuration.include Mongoid::Matchers in your rspec. See the mongoid-rspec gem for use.

Step The Second: Extract the mongoid definitions

require 'spec_helper'

module Contactable

  def self.included(receiver) 
    receiver.class_eval do
      field :first_name, type: String
      field :last_name, type: String
      field :phone_number, type: String
      field :address_line_1, type: String
      field :city, type: String
      field :state, type: String
      field :postal_code, type: String
      field :email, type: String
      validates_presence_of :first_name
      validates_presence_of :last_name
    end
  end
end

class Doctor
  include Mongoid::Document
  include Mongoid::Timestamps
  include Contactable
end

And run those tests!

....

Finished in 0.11461 seconds
4 examples, 0 failures

Step 3: Extract the Tests!

We’ll extract the tests out into a shared_examples file in the support folder, and then tell the Doctor class that it should behave like a Contact.

#spec/support/shared_examples.rb
shared_examples_for Contactable do
    it { should have_fields(:first_name, :last_name) }
    it { should have_fields(:phone_number, :email, :address_line_1, :city, :state, :postal_code) }
    it { should validate_presence_of(:first_name) }
    it { should validate_presence_of(:last_name) }
end

#spec/models/doctor_spec.rb

require 'spec_helper'
describe Doctor do
    it_behaves_like Contactable
end

Run those tests! Could be faster

....

Finished in 0.13347 seconds
4 examples, 0 failures

All is going awesome! So we can now easily add contact information (and validations), to say users:

class User
  include Mongoid::Document
  include Mongoid::Timestamps
  include Contactable
end

describe User do
  it_behaves_like Contactable
end

Now your Users have first_name, last_name, address, and more!

Let’s Take this to 11

Now we can very, very easily isolate the Doctor out for very fast tests.

module Mongoid
    module Document; end
  module Timestamps; end
end
class Pharmacy; end

require_relative "../../app/models/doctor"
require_relative "support/shared_examples"

describe Doctor do
  it_behaves_like Contactable

    it "will tell the pharmacy to release the rx's" do
        Pharmacy.should_receive(:release_the_rx!)
        subject.gimme!
    end
end

The above would fail since #gimme! doesn’t exist, but it would be:

In total isolation from Rails
Total isolation from Mongo DB
fast!

I created the following to easily add re-usable data-bags to documents in Mongoid, rather than copying and pasting. The same shared-example technique works well in ActiveRecord.

Some Assumptions Before We Begin

Step 1: Write those tests first

Step The Second: Extract the mongoid definitions

Step 3: Extract the Tests!

Let’s Take this to 11

Version Disclosure: written against mongoid-rspec 1.4, mongoid 2.4, rspec 2.8.