A Live Web Application

By Michael Hartl
Oct 25, 2022

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10.3 Layouts

At this point, our app is looking pretty good, but there are two significant blemishes: The HTML code for the three pages is highly repetitive, and navigating by hand from page to page is rather cumbersome. We’ll fix the first blemish in this section, and the second in Section 10.4. (And of course our app doesn’t yet detect palindromes, which is the subject of Section 10.5.)

If you followed Learn Enough CSS & Layout to Be Dangerous, you’ll know that the Layout in the title referred to page layout generally—using Cascading Style Sheets to move elements around on the page, align them properly, etc.— but we also saw that doing this properly requires defining layout templates that capture common patterns and eliminate duplication.

In the present case, each of our site’s pages has the same basic structure, as shown in Listing 10.10.

Listing 10.10: The HTML structure of our site’s pages.

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Learn Enough Ruby Sample App</title>
    <link rel="stylesheet" type="text/css" href="/stylesheets/main.css">
    <link href="https://fonts.googleapis.com/css?family=Open+Sans:300,400"
          rel="stylesheet">
  </head>
  <body>
    <a href="/" class="header-logo">
      <img src="/images/logo_b.png" alt="Learn Enough logo">
    </a>
    <div class="container">
      <div class="content">

        <!-- page-specific content -->
      </div>
    </div>
  </body>
</html>

Everything except the page-specific content (indicated by the highlighted HTML comment) is the same on each page. In Learn Enough CSS & Layout to Be Dangerous, we eliminated this duplication using Jekyll templates; in this tutorial, we’ll use Sinatra layouts instead.

Now, our site is currently working, in the sense that each page has the proper content at this stage of development. We’re about to make a change that involves moving around and deleting a bunch of HTML, and we’d like to do this without breaking the site. Does that sound like something we’ve seen before?

It does indeed. This is exactly the kind of problem we faced in Chapter 8 when we developed and then refactored the palindrome gem. In that case, we wrote automated tests to catch any regressions, and in this case we’re going to do the same. (I started making websites long before automated testing of web applications was possible, much less the norm, and believe me, automated tests are a huge improvement over testing web apps by hand.)

To get started, we’ll add some more gems to our Gemfile, this time in a group called :test that indicates gems that are needed only for tests. The result appears in Listing 10.11.

Listing 10.11: Adding gems for testing.
`Gemfile`

source 'https://rubygems.org'

ruby '3.1.1'   # Change this line if you're using a different Ruby version.

gem 'sinatra', '2.2.0'
gem 'puma',    '5.6.4'
gem 'rerun',   '0.13.1'

group :test do
   gem 'minitest',             '5.15.0'
   gem 'minitest-reporters',   '1.5.0'
   gem 'rack-test',            '1.1.0'

   gem 'rake',                 '13.0.6'
   gem 'nokogiri',             '1.13.3'
end

We then install the gems as usual:

$  bundle _2.3.10_ install

If you encounter an error while installing nokogiri (which is unfortunately common), you’ll have to apply your technical sophistication (Box 1.1) to resolve the issue; I especially recommend the “Google the error message” algorithm for this case.

We’ll factor out common elements needed in all tests into a test helper file, while also creating a file for our initial site pages tests:

$ mkdir test
$ touch test/test_helper.rb test/site_pages_test.rb

The test helper requires all the necessary gems, and also includes the app itself using require_relative, which requires files relative to the current directory. The result appears in Listing 10.12.

Listing 10.12: The initial test helper.
`test/test_helper.rb`

ENV['RACK_ENV'] = 'test'

require_relative '../app'
require 'rack/test'
require 'nokogiri'
require 'minitest/autorun'
require 'minitest/reporters'
Minitest::Reporters.use!

We then need to create a Rakefile to tell the rake utility how to run the tests:

$ touch Rakefile

The contents are shown in Listing 10.13.

Listing 10.13: Configuring `rake` to run tests.
`Rakefile`

require 'rake/testtask'

Rake::TestTask.new do |t| t.pattern = 'test/*_test.rb' t.warning = false end task :default => [:test]

We’ll put the result of Listing 10.13 to good use in a moment, but first we need to write some tests. We’ll start with super-basic tests so that the app serves up something, as indicated by the HTTP response code 200 (OK), which we can do like this:

def test_index
  get '/'
  assert last_response.ok?
end

Here we use the get command in the test to issue a GET request to the root URL /, which automatically creates an object called last_response as a side effect. We can then use a minitest assertion (Section 8.2) using the boolean method ok?, which is also available automatically. The result is a test that makes sure the server responded properly to the request.

Applying the above discussion to the About and Palindrome Detector pages as well, and combining them with configuration code pulled right from the official Sinatra documentation on tests, we arrive at our initial test suite, shown in Listing 10.14.

Listing 10.14: Our initial test suite. GREEN
`test/site_pages_test.rb`

require_relative 'test_helper'

class PalindromeAppTest < Minitest::Test
  include Rack::Test::Methods

  def app
    Sinatra::Application
  end

  def test_index
    get '/'
    assert last_response.ok?
  end

  def test_about
    get '/about'
    assert last_response.ok?
  end

  def test_palindrome
    get '/palindrome'
    assert last_response.ok?
  end
end

With the setup in Listing 10.13, we can use rake to execute the test suite as follows:

Listing 10.15: GREEN

$ bundle exec rake test
3 tests, 3 assertions, 0 failures, 0 errors, 0 skips

Also note that Listing 10.13 has followed the common Ruby convention of making running the test suite the default (an indication of how important tests are in the Ruby community), so we can actually just run rake by itself:³

Listing 10.16: GREEN

$ bundle exec rake
3 tests, 3 assertions, 0 failures, 0 errors, 0 skips

We’ll continue to use rake test for clarity, but it’s good to know about this alternative convention.

The tests in Listing 10.14 are a fine start, but they really only check if the pages are there at all. It would be nice to have a slightly more stringent test of the HTML content, though not too stringent—we don’t want our tests to make it hard to make changes in the future. As a middle ground, we’ll check that each page in the site has an h1 tag somewhere in the document.

In order to do this, we’ll write a short function in test_helper.rb to return a doc object, akin to the document object in JavaScript. We actually already know pretty much how to make it based on our work in Section 9.3, where we saw how to use Nokogiri to create a document from HTML, like this:

Nokogiri::HTML(html)

The only extra ingredient is the knowledge that Sinatra’s HTTP response objects always have a body attribute representing the HTML body (the full page, not just the body tag). This means we can define doc as shown in Listing 10.17.

Listing 10.17: What’s up, Doc?
`test/test_helper.rb`

ENV['RACK_ENV'] = 'test'

require_relative '../app'
require 'rack/test'
require 'nokogiri'
require 'minitest/autorun'
require 'minitest/reporters'
Minitest::Reporters.use!

# Returns the document.
def doc(response)

  Nokogiri::HTML(response.body)
end

Now we’re ready to use doc to find the h1 (if any) on the page. One possibility would be to use doc.css as in, e.g., Listing 9.12:

doc(last_response).css('h1')

In the present case, though, we only need to see if there’s any h1 tag, so we only need the first element:

doc(last_response).css('h1').first

This would work fine, but this is such a common case that Nokogiri has a special method for it, called at_css:

doc(last_response).at_css('h1')

Because this will be nil if there’s no h1 and non-nil otherwise, we can use a simple assertion, like this:

assert doc(last_response).at_css('h1')

Adding this to each page in our site yields the updated test suite shown in Listing 10.18.

Listing 10.18: Adding assertions for the presence of an `h1` tag. GREEN
`test/site_pages_test.rb`

require_relative 'test_helper'

class PalindromeAppTest < Minitest::Test
  include Rack::Test::Methods

  def app
    Sinatra::Application
  end


  def test_index
    get '/'
    assert last_response.ok?
    assert doc(last_response).at_css('h1')
  end

  def test_about
    get '/about'
    assert last_response.ok?
    assert doc(last_response).at_css('h1')
  end

  def test_palindrome
    get '/palindrome'
    assert last_response.ok?
    assert doc(last_response).at_css('h1')
  end
end

By the way, some programmers adopt the convention of only ever having one assertion per test, whereas in Listing 10.18 we have two. In my experience, the overhead associated with setting up the right state (e.g., duplicating the calls to get) makes this convention inconvenient, and I’ve never run into any trouble from including multiple assertions in a test.

The tests in Listing 10.18 should now be GREEN as required:

Listing 10.19: GREEN

$ bundle exec rake test
3 tests, 6 assertions, 0 failures, 0 errors, 0 skips

At this point, we’re ready to use a Sinatra layout to eliminate duplication. Our first step is to remove the extraneous material from our pages, leaving only the core content, as shown in Listing 10.20, Listing 10.21, and Listing 10.22. (This is why the body content wasn’t fully indented before.)

Listing 10.20: The core Home (index) view.
`views/index.erb`

<h1>Sample Sinatra App</h1>


<p>
  This is the sample Sinatra app for
  <a href="https://www.learnenough.com/ruby-tutorial"><em>Learn Enough Ruby
  to Be Dangerous</em></a>. Learn more on the <a href="/about">About</a> page.
</p>

<p>
  Click the <a href="https://en.wikipedia.org/wiki/Sator_Square">Sator
  Square</a> below to run the custom <a href="/palindrome">Palindrome
  Detector</a>.
</p>

<a class="sator-square" href="/palindrome">
  <img src="/images/sator_square.jpg" alt="Sator Square">
</a>

Listing 10.21: The core About view.
`views/about.erb`

<h1>About</h1>

<p>
  This site is the final application in
  <a href="https://www.learnenough.com/ruby-tutorial"><em>Learn Enough Ruby
  to Be Dangerous</em></a>
  by <a href="https://www.michaelhartl.com/">Michael Hartl</a>,
  a tutorial introduction to the
  <a href="https://www.ruby-lang.org/en/">Ruby programming language</a> that
  is part of
  <a href="https://www.learnenough.com/">LearnEnough.com</a>.
</p>

<p>
  <em>Learn Enough Ruby to Be Dangerous</em> is a natural prerequisite to
  the <a href="https://www.railstutorial.org/"><em>Ruby on Rails
  Tutorial</em></a>, a book and video series that is one of the leading
  introductions to web development. <em>Learn Enough Ruby</em> is also an
  excellent choice <em>after</em> the <em>Rails Tutorial</em> for those who
  prefer to start with the latter first.
</p>

Listing 10.22: The core Palindrome Detector view.
`views/palindrome.erb`

<h1>Palindrome Detector</h1>

<p>This will be the palindrome detector.</p>

Having stripped all the layout material from our pages, we’ll now create a file called layout.erb in the views directory that restores it:

$ touch views/layout.erb

Let’s start by filling it with the same content as the schematic HTML structure we saw in Listing 10.10, as seen in Listing 10.23.

Listing 10.23: Using an initial (incorrect) schematic layout. RED
`views/layout.erb`

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Learn Enough Ruby Sample App</title>
    <link rel="stylesheet" type="text/css" href="/stylesheets/main.css">
    <link href="https://fonts.googleapis.com/css?family=Open+Sans:300,400"
          rel="stylesheet">
  </head>
  <body>
    <a href="/" class="header-logo">
      <img src="/images/logo_b.png" alt="Learn Enough logo">
    </a>
    <div class="container">
      <div class="content">
        <!-- page-specific content -->
      </div>
    </div>
  </body>
</html>

As indicated in the caption to Listing 10.23, this layout breaks our test suite:

Listing 10.24: RED

$ bundle exec rake test
3 tests, 6 assertions, 3 failures, 0 errors, 0 skips

The ok? assertions in Listing 10.18 are passing, but the h1 assertions are failing. This is because the site is now a bare layout, as shown in Figure 10.8.

Figure 10.8: The bare layout, with no content.

To get the tests to pass and restore our site to full functionality, all we need to do is replace the HTML comment

<!-- page-specific content -->

with some special Ruby code:

<%= yield %>

This is our first example of embedded Ruby, which we’ll learn more about in Section 10.4. The special <%= ... %> notation arranges to evaluate the code represented by ... and insert it into the site.

In this case, that code is yield, the keyword used in Section 5.4.1 to yield content to a block, but the truth is that I don’t know offhand exactly how this works or precisely why a block is involved. Indeed, I encourage you to think of <%= yield %> as meaning “special code that inserts the page content into a layout”, and not worry about the details. (If you do much Ruby web development, you’ll soon get used to it—the exact same code is used in Ruby on Rails application layouts.)

Making the replacement suggested above yields (heh) the layout shown in Listing 10.25.

Listing 10.25: Inserting content into the site layout. GREEN
`views/layout.erb`

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Learn Enough Ruby Sample App</title>
    <link rel="stylesheet" type="text/css" href="/stylesheets/main.css">
    <link href="https://fonts.googleapis.com/css?family=Open+Sans:300,400"
          rel="stylesheet">
  </head>
  <body>
    <a href="/" class="header-logo">
      <img src="/images/logo_b.png" alt="Learn Enough logo">

      </a>
      <div class="container">
        <div class="content">
          <%= yield %>
        </div>
      </div>
    </body>
</html>

With that, our layout is working, the horrible repeated code has been eliminated, and our tests are GREEN:

Listing 10.26: GREEN

$ bundle exec rake test
3 tests, 6 assertions, 0 failures, 0 errors, 0 skips

A quick check in the browser confirms that things are working as expected (Figure 10.9).

Figure 10.9: Our Home page, now created using a layout.

By the way, it’s worth noting that we could have used a layout file called, say, views/page.erb, in which case we would have had to update app.rb with an explicit hash option telling each page to use that file for the layout:

require 'sinatra'

get '/' do
  erb :index, :layout => :page
end

get '/about' do
  erb :about, :layout => :page
end

get '/palindrome' do
  erb :palindrome, :layout => :page
end

(Note that Ruby allows us to omit curly braces on hashes when they’re the last argument to a function.) When the layout file has the special name layout.-erb, though, Sinatra knows to look for it by default, so we can omit it in the app file. This sort of practice foreshadows the “convention over configuration” philosophy adopted and popularized by Ruby on Rails.

10.3.1 Exercises

As you can confirm by running the source of any page through an HTML validator, the current pages are valid HTML, but there’s a warning with a suggestion to add a lang (language) attribute to the html tag. Add the attribute lang="en" (for “English”) to the html tag in Listing 10.25 and confirm using a web inspector that it appears correctly on all three pages.
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