Add Articles show and fix fixtures

Add the capability to show a single article and fix errors in multiline
fixtures to make controller test assertsions pass.

* Add the Articles show route
* Add the show action to the ArticlesController
* Add the show.html.erb view
* Modify the index view to link to each article
* Fix the fixtures to properly fold multiline text for the Article body

Completes Rails Getting Started Guide:
* 7 CRUDit Where CRUDit Is Due
  * 7.1 Showing a Single Article

app/controllers/articles_controller.rb

@@ -2,4 +2,8 @@ class ArticlesController < ApplicationController
   def index
     @articles = Article.all
   end
+
+  def show
+    @article = Article.find(params[:id])
+  end
 end

app/views/articles/index.html.erb

@@ -3,7 +3,9 @@
 <ul>
   <% @articles.each do |article| %>
     <li>
-      <%= article.title %>
+      <a href="/articles/<%= article.id %>">
+        <%= article.title %>
+      </a>
     </li>
   <% end %>
 </ul>

app/views/articles/show.html.erb

@@ -0,0 +1,3 @@
+<h1><%= @article.title %></h1>
+
+<p><%= @article.body %></p>

config/routes.rb

@@ -2,4 +2,5 @@
   root "articles#index"
 
   get "/articles", to: "articles#index"
+  get "/articles/:id", to: "articles#show"
 end

test/controllers/articles_controller_test.rb

@@ -1,10 +1,21 @@
 require "test_helper"
 
 class ArticlesControllerTest < ActionDispatch::IntegrationTest
+  def setup
+    @article = articles(:nerd)
+  end
+
   test "should get index" do
     get articles_url
     assert_response :success
     assert_select 'h1', 'Articles'
     assert_select 'li', Article.count
   end
+
+  test "should get show" do
+    get "/articles/#{@article.id}"
+    assert_response :success
+    assert_select 'h1', @article.title
+    assert_select 'p', @article.body
+  end
 end

test/fixtures/articles.yml

@@ -2,15 +2,14 @@
 
 nerd:
   title: Check out NerdDice
-  body: |
+  body: >-
     These videos take you end-to-end through a project that creates a ruby gem.
     (The subject matter of polyhedral dice was chosen because Mike\'s a giant nerd.)
     The series covers a number of programming concepts that will help you be a better
     software developer, particularly in Ruby.
-
 why:
   title: Why Stateless Code
-  body: |
+  body: >-
     Inspired by Simon Sinek\'s brilliant video Start with Why, these videos explain the
     North Star of Stateless Code. What gets us out of bed in the morning and motivates
     us to keep producing videos? Why do we do what we do? What is the dream for this