Add component testing

Gemfile

@@ -43,6 +43,7 @@ group :test do
   gem "i18n-coverage"
   gem "minitest-reporters"
   gem "mocha"
+  gem "shoulda-context"
   gem "simplecov"
   gem "timecop"
   gem "webmock", require: false

Gemfile.lock

@@ -567,6 +567,7 @@ GEM
       concurrent-ruby (~> 1.0, >= 1.0.2)
     sentry-ruby-core (5.3.1)
       concurrent-ruby
+    shoulda-context (2.0.0)
     simplecov (0.22.0)
       docile (~> 1.1)
       simplecov-html (~> 0.11)
@@ -646,6 +647,7 @@ DEPENDENCIES
   rss
   rubocop-govuk
   sassc-rails
+  shoulda-context
   simplecov
   slimmer
   sprockets-rails

test/components/all_components_test.rb

@@ -0,0 +1,57 @@
+require "test_helper"
+
+class AllComponentsTest < ActionController::TestCase
+  Dir.glob("app/views/components/*.erb").each do |filename|
+    template = filename.split("/").last
+    component_name = template.sub("_", "").sub(".html", "").sub(".erb", "").gsub("-", "_")
+
+    context component_name do
+      yaml_file = "#{__dir__}/../../app/views/components/docs/#{component_name}.yml"
+
+      should "is documented" do
+        assert File.exist?(yaml_file)
+      end
+
+      should "have the correct documentation" do
+        yaml = YAML.unsafe_load_file(yaml_file)
+
+        assert yaml["name"]
+        assert yaml["description"]
+        assert yaml["examples"]
+        assert yaml["accessibility_criteria"] || yaml["shared_accessibility_criteria"]
+      end
+
+      should "have the correct class in the ERB template" do
+        erb = File.read(filename)
+
+        class_name = "app-c-#{component_name.dasherize}"
+
+        assert_includes erb, class_name
+      end
+
+      should "have a correctly named template file" do
+        template_file = "#{__dir__}/../../app/views/components/_#{component_name}.html.erb"
+
+        assert File.exist?(template_file)
+      end
+
+      should "have a correctly named spec file" do
+        rspec_file = "#{__dir__}/../../test/components/#{component_name.tr('-', '_')}_test.rb"
+
+        assert File.exist?(rspec_file)
+      end
+
+      should "have a correctly named SCSS file" do
+        css_file = "#{__dir__}/../../app/assets/stylesheets/components/_#{component_name.tr('_', '-')}.scss"
+
+        assert File.exist?(css_file)
+      end
+
+      should "not use `html_safe`", not_applicable: component_name.in?(%w[govspeak]) do
+        file = File.read(filename)
+
+        assert_no_match file, "html_safe"
+      end
+    end
+  end
+end