Add accessibility testing via aXe

These tests will look for the class '.js-test-a11y' and run axe against them,
it'll then throw an error to be caught in dev tools or better in an applications'
integration tests.

DEVELOPMENT.md

@@ -0,0 +1,15 @@
+### Running tests
+
+The default rake task runs all tests:
+```
+bundle exec rake
+```
+
+Javascript is tested using Jasmine and the [Jasmine gem](https://github.com/pivotal/jasmine-gem). Tests can be run either in the browser or on the command line via the dummy app’s tasks:
+```sh
+# browser
+bundle exec rake app:jasmine
+
+# command line
+bundle exec rake app:jasmine:ci
+```

README.md

@@ -84,3 +84,6 @@ This will create a template, scss file and yml documentation file for a new comp
 ## Licence
 
 [MIT Licence](LICENCE.md)
+
+## Development
+For documentation on how to update and develop this gem see [DEVELOPMENT.md](./DEVELOPMENT.md)

Rakefile

@@ -2,15 +2,11 @@ require 'rspec/core/rake_task'
 RSpec::Core::RakeTask.new(:spec)
 
 APP_RAKEFILE = File.expand_path("../test/dummy/Rakefile", __FILE__)
-load 'rails/tasks/engine.rake'
-
 
+load 'rails/tasks/engine.rake'
 load 'rails/tasks/statistics.rake'
 
-
-
 require 'bundler/gem_tasks'
-
 require 'rake/testtask'
 
 Rake::TestTask.new(:test) do |t|
@@ -32,4 +28,4 @@ namespace :assets do
   end
 end
 
-task default: :spec
+task default: [:spec, 'app:jasmine:ci']

app/assets/javascripts/govuk_publishing_components/accessibility-test.js

@@ -0,0 +1,78 @@
+(function (window, document, axe) {
+  window.GOVUK = window.GOVUK || {}
+
+  function AccessibilityTest (selector, callback) {
+    if (typeof callback !== 'function') {
+      return
+    }
+
+    if (!document.querySelector(selector)) {
+      return callback('No selector "' + selector + '" found')
+    }
+
+    var axeOptions = {
+      restoreScroll: true,
+      include: [selector]
+    }
+    axe.run(axeOptions, function (err, results, blah, boo) {
+      if (err) {
+        callback('aXe Error: ' + err)
+      }
+
+      var violations = (typeof results === 'undefined') ? [] : results.violations
+
+      if (violations.length === 0) {
+        return callback('No accessibility issues found')
+      }
+
+      var errorText = (
+        '\n' + 'Accessibility issues at ' +
+        results.url + '\n\n' +
+        violations.map(function (violation) {
+          var help = 'Problem: ' + violation.help
+          var helpUrl = 'Try fixing it with this help: ' + violation.helpUrl
+          var htmlAndTarget = violation.nodes.map(_renderNode).join('\n\n')
+
+          return [
+            help,
+            htmlAndTarget,
+            helpUrl
+          ].join('\n\n\n')
+        }).join('\n\n- - -\n\n')
+      )
+      callback(undefined, errorText)
+    })
+  }
+
+  var _renderNode = function (node) {
+    return (
+      ' Check the HTML:\n' +
+      ' `' + node.html + '`\n' +
+      ' found with the selector:\n' +
+      ' "' + node.target.join(', ') + '"'
+    )
+  }
+
+  var _throwUncaughtError = function (error) {
+    // aXe swallows throw errors so we pass it through a setTimeout
+    // so that it's not in aXe's context
+    setTimeout(function () {
+      throw new Error(error)
+    }, 0)
+  }
+
+  window.GOVUK.AccessibilityTest = AccessibilityTest
+
+  // Cut the mustard at IE9+ since aXe only works with those browsers.
+  // http://responsivenews.co.uk/post/18948466399/cutting-the-mustard
+  if (document.addEventListener) {
+    document.addEventListener('DOMContentLoaded', function () {
+      AccessibilityTest('.js-test-a11y', function (err, results) {
+        if (err) {
+          return
+        }
+        _throwUncaughtError(results)
+      })
+    })
+  }
+})(window, document, window.axe)

app/assets/javascripts/govuk_publishing_components/application.js

@@ -10,4 +10,5 @@
 // Read Sprockets README (https://github.com/rails/sprockets#sprockets-directives) for details
 // about supported directives.
 //
+//= require_tree ./vendor
 //= require_tree .

app/assets/stylesheets/govuk_publishing_components/component_guide.scss

@@ -166,4 +166,3 @@ html {
     }
   }
 }
-

app/views/govuk_publishing_components/component_guide/component_doc/_preview.html.erb

@@ -1,3 +1,3 @@
-<div class="component-guide-preview">
+<div class="js-test-a11y component-guide-preview">
   <%= render @component_doc.partial_path, fixture.html_safe_data %>
 </div>

app/views/govuk_publishing_components/component_guide/preview.html.erb

@@ -3,6 +3,8 @@
     <% if @component_fixtures.length > 1 %>
       <h2 class="preview-title"><a href="<%= component_fixture_path(@component_doc.id, fixture.id) %>"><%= fixture.name %></a></h2>
     <% end %>
-    <%= render @component_doc.partial_path, fixture.html_safe_data %>
+    <div class="js-test-a11y">
+      <%= render @component_doc.partial_path, fixture.html_safe_data %>
+    </div>
   </div>
 <% end %>

govuk_publishing_components.gemspec

@@ -14,7 +14,7 @@ Gem::Specification.new do |s|
   s.homepage    = "https://github.com/alphagov/govuk_publishing_components"
   s.license     = "MIT"
 
-  s.files = Dir["{app,config,db,lib}/**/*", "LICENCE.md", "Rakefile", "README.md"]
+  s.files = Dir["{app,config,db,lib}/**/*", "DEVELOPMENT.md", "LICENCE.md", "Rakefile", "README.md"]
 
   s.add_dependency "rails", ">= 5.0.0.1"
   s.add_dependency "slimmer"
@@ -25,6 +25,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "govuk-lint", "~> 2.1.0"
   s.add_development_dependency "rspec", "~> 3.6"
   s.add_development_dependency "capybara", "~> 2.14.4"
+  s.add_development_dependency "jasmine", "~> 2.4.0"
 
   # Needed to load slimmer test helpers
   # https://github.com/alphagov/slimmer/issues/201

spec/component_guide/component_guide_spec.rb

@@ -110,6 +110,11 @@
     end
   end
 
+  it 'has accessibility testing hooks' do
+    visit '/component-guide/test-component'
+    expect(page).to have_selector('.component-guide-preview.js-test-a11y')
+  end
+
   it 'displays the accessibility acceptance criteria of a component as html using static’s govspeak component' do
     visit '/component-guide/test-component'
     within ".component-accessibility-criteria" do
@@ -132,6 +137,7 @@
     expect(page).to have_selector('.component-guide-preview-page .test-component-with-params', text: 'Some value')
     expect(page).to have_selector('.component-guide-preview-page .preview-title', text: 'Another fixture')
     expect(page).to have_selector('.component-guide-preview-page .test-component-with-params', text: 'A different value')
+    expect(page).to have_selector('.component-guide-preview-page .js-test-a11y')
   end
 
   it 'loads a preview page for a specific fixture' do
@@ -142,5 +148,6 @@
 
     expect(page).to have_no_selector('.component-guide-preview-page .preview-title')
     expect(page).to have_selector('.component-guide-preview-page .test-component-with-params', text: 'A different value')
+    expect(page).to have_selector('.component-guide-preview-page .js-test-a11y')
   end
 end

spec/javascripts/govuk_publishing_components/AccessibilityTestSpec.js

@@ -0,0 +1,139 @@
+/* global jasmine, describe, afterEach, beforeEach, it, expect */
+
+var AccessibilityTest = window.GOVUK.AccessibilityTest
+
+function addToDom (html, style) {
+  var div = document.createElement('div')
+  var htmlToInject = ''
+  if (style) {
+    htmlToInject += '<style>' + style + '</style>'
+  }
+  htmlToInject += '<div class="js-test-a11y">' + html + '</div>'
+  div.innerHTML = htmlToInject
+  document.getElementsByTagName('body')[0].appendChild(div)
+}
+
+function removeFromDom (selector) {
+  var nodeToRemove = document.querySelector(selector)
+  if (nodeToRemove) {
+    nodeToRemove.parentNode.removeChild(nodeToRemove)
+  }
+}
+
+function renderErrorMessage (option) {
+  var url = window.location.href
+  var message = ''
+  if (!option.skipHeader) {
+    message += '\nAccessibility issues at ' + url + '\n\n'
+  }
+  message += (
+    'Problem: ' + option.problem + '\n' +
+    '\n' +
+    '\n' +
+    ' Check the HTML:\n' +
+    ' `' + option.html + '`\n' +
+    ' found with the selector:\n' +
+    ' "' + option.selector + '"\n' +
+    '\n' +
+    '\n' +
+    'Try fixing it with this help: ' + option.helpUrl
+  )
+  return message
+}
+
+describe('AccessibilityTest', function () {
+  var selector = '.js-test-a11y'
+
+  beforeEach(function () {
+    jasmine.DEFAULT_TIMEOUT_INTERVAL = 11000
+  })
+
+  afterEach(function () {
+    removeFromDom(selector)
+  })
+
+  it('should do nothing if no callback is specified', function () {
+    AccessibilityTest(selector)
+  })
+
+  it('should error if no selector is found', function (done) {
+    AccessibilityTest(selector, function (err, result) {
+      expect(result).toBe(undefined)
+      expect(err).toBe('No selector "' + selector + '" found')
+      done()
+    })
+  })
+
+  it('should throw if there\'s a contrast issue', function (done) {
+    addToDom('<a href="#">Low contrast</a>', 'a { background: white; color: #ddd }')
+
+    AccessibilityTest(selector, function (err, result) {
+      if (err) {
+        throw err
+      }
+
+      var errorMessage = renderErrorMessage({
+        problem: 'Elements must have sufficient color contrast',
+        html: '<a href="#" style="">Low contrast</a>',
+        selector: '.js-test-a11y > a',
+        helpUrl: 'https://dequeuniversity.com/rules/axe/3.0.0-alpha/color-contrast?application=axeAPI'
+      })
+
+      expect(result).toBe(errorMessage)
+
+      done()
+    })
+  })
+
+  it('should throw if there\'s a alt tag issue', function (done) {
+    addToDom('<img src="">')
+
+    AccessibilityTest(selector, function (err, result) {
+      if (err) {
+        throw err
+      }
+
+      var errorMessage = renderErrorMessage({
+        problem: 'Images must have alternate text',
+        html: '<img src="">',
+        selector: '.js-test-a11y > img',
+        helpUrl: 'https://dequeuniversity.com/rules/axe/3.0.0-alpha/image-alt?application=axeAPI'
+      })
+
+      expect(result).toBe(errorMessage)
+
+      done()
+    })
+  })
+
+  it('should throw on multiple issues', function (done) {
+    addToDom('<img src=""><a href="#">Low contrast</a>', 'a { background: white; color: #ddd }')
+
+    AccessibilityTest(selector, function (err, result) {
+      if (err) {
+        throw err
+      }
+
+      var errorMessage = (
+        renderErrorMessage({
+          problem: 'Elements must have sufficient color contrast',
+          html: '<a href="#" style="">Low contrast</a>',
+          selector: '.js-test-a11y > a',
+          helpUrl: 'https://dequeuniversity.com/rules/axe/3.0.0-alpha/color-contrast?application=axeAPI'
+        }) +
+        '\n\n- - -\n\n' +
+        renderErrorMessage({
+          skipHeader: true,
+          problem: 'Images must have alternate text',
+          html: '<img src="">',
+          selector: '.js-test-a11y > img',
+          helpUrl: 'https://dequeuniversity.com/rules/axe/3.0.0-alpha/image-alt?application=axeAPI'
+        })
+      )
+
+      expect(result).toBe(errorMessage)
+
+      done()
+    })
+  })
+})