Wait a minute! It’s a post, man.

We’ll start with the Post model first. I’ll keep the commentary to a minimum because you know this stuff already.

rails generate model Post title:string body:text
rails db:migrate

We’ll need a test framework. I like Minitest.

# Gemfile 
gem 'minitest', group: :test

bundle install

I use TDD but you can do whatever you like. I’m not your dad.

I’ll fast-forward through the details.

require 'test_helper'
class PostTest < ActiveSupport::TestCase
  test 'a post has a title and a body' do
    post = Post.create! title: 'The title', body: 'The body.'
    assert_equal 'The title', post.title
    assert_equal 'The body.', post.body
  end
end

rails test

.E

Error:
PostsControllerTest#test_should_get_index:
NameError: undefined local variable or method `posts_index_url' for #<PostsControllerTest:0x00007f8939850650>
    test/controllers/posts_controller_test.rb:5:in `block in <class:PostsControllerTest>'

PostTest passes already but the auto-generated PostControllerTest is failing because the path is wrong. Let’s fix that.

require 'test_helper'
class PostsControllerTest < ActionDispatch::IntegrationTest
  test 'should get index' do
    get posts_url
    assert_response :success
  end
end

rails test

# Running:

..

Finished in 0.382970s, 5.2223 runs/s, 7.8335 assertions/s.
2 runs, 3 assertions, 0 failures, 0 errors, 0 skips

Our React app is going to need some JSON. Let’s add a show action to PostsController.

require 'test_helper'
class PostsControllerTest < ActionDispatch::IntegrationTest
  setup do
    @post = Post.create! title: 'The title', body: 'The body.'
  end

  test 'fetch a post as json' do
    get post_url(@post, format: :json)
    assert_response :success

    json = JSON.parse response.body, symbolize_names: true
    assert_equal @post.id, json[:id]
    assert_equal 'The title', json[:title]
    assert_equal 'The body.', json[:body]
  end
end

# PostsController.rb
class PostsController < ApplicationController
  before_action :set_post, only: :show
  
  private
  def set_post
    @post = Post.find params[:id]
  end
end

# views/posts/show.json.jbuilder
json.extract! @post, :id, :title, :body, :created_at, :updated_at

Let’s create a post so we can see what the JSON looks like.

# In the rails console
Post.create! title: 'React on Rails', body: 'I can use React with Rails.'

open http://localhost:3000/posts/1.json

That’s the back-end taken care of. We’ll build a React component to show our post in the next instalment.