Pure RSpec JSON API testing

Testing Serializer object and introducing it to Controller

Let say you want to build your API to comply jsonapi.org specification and the result should look like:

{
  "article": {
    "id": "305",
    "type": "articles",
    "attributes": {
      "title": "Asking Alexandria"
    }
  }
}

Test for Serializer object may look like this:

# spec/serializers/article_serializer_spec.rb

require 'rails_helper'

RSpec.describe ArticleSerializer do
  subject { described_class.new(article) }
  let(:article) { instance_double(Article, id: 678, title: "Bring Me The Horizon") }

  describe "#as_json" do
    let(:result) { subject.as_json }

    it 'root should be article Hash' do
      expect(result).to match({
        article: be_kind_of(Hash)
      })
    end

    context 'article hash' do
      let(:article_hash) { result.fetch(:article) }

      it 'should contain type and id' do
        expect(article_hash).to match({
          id: article.id.to_s,
          type: 'articles',
          attributes: be_kind_of(Hash)
        })
      end

      context 'attributes' do
        let(:article_hash_attributes) { article_hash.fetch(:attributes) }

        it do
          expect(article_hash_attributes).to match({
            title: /[Hh]orizon/,
          })
        end
      end
    end
  end
end

Serializer object may look like this:

# app/serializers/article_serializer.rb

class ArticleSerializer
  attr_reader :article

  def initialize(article)
    @article = article
  end

  def as_json
    {
      article: {
        id: article.id.to_s,
        type: 'articles',
        attributes: {
          title: article.title
        }
      }
    }
  end
end

When we run our “serializers” specs everything passes.

That’s pretty boring. Let’s introduce a typo to our Article Serializer: Instead of type: "articles" let’s return type: "events" and rerun our tests.

rspec spec/serializers/article_serializer_spec.rb

.F.

Failures:

  1) ArticleSerializer#as_json article hash should contain type and id
     Failure/Error:
       expect(article_hash).to match({
         id: article.id.to_s,
         type: 'articles',
         attributes: be_kind_of(Hash)
       })
     
       expected {:id=>"678", :type=>"event",
:attributes=>{:title=>"Bring Me The Horizon"}} to match {:id=>"678",
:type=>"articles", :attributes=>(be a kind of Hash)}
       Diff:
       
       @@ -1,4 +1,4 @@
       -:attributes => (be a kind of Hash),
       +:attributes => {:title=>"Bring Me The Horizon"},
        :id => "678",
       -:type => "articles",
       +:type => "events",
       
     # ./spec/serializers/article_serializer_spec.rb:20:in `block (4
levels) in <top (required)>'

Once you’ve run the test it’s pretty easy to spot the error.

Once you fix the error (correct the type to be article) you can introduce it to Controller like this:

# app/controllers/v2/articles_controller.rb
module V2
  class ArticlesController < ApplicationController
    def show
      render json: serializer.as_json
    end

    private
      def article
        @article ||= Article.find(params[:id])
      end

      def serializer
        @serializer ||= ArticleSerializer.new(article)
      end
  end
end

This example is based on article: https://www.eq8.eu/blogs/30-pure-rspec-json-api-testing