Adds locale switcher js code + feature tests

spec/features/locale_switcher_spec.rb

@@ -0,0 +1,29 @@
+require 'rails_helper'
+
+feature 'Locale Switcher' do
+
+  scenario 'Available locales appear in the locale switcher' do
+    visit '/'
+
+    within('.js-locale-switcher') do
+      expect(page).to have_content 'Español'
+      expect(page).to have_content 'English'
+    end
+  end
+
+  scenario 'The current locale is selected' do
+    visit '/'
+    expect(page).to have_select('locale-switcher', selected: 'English')
+  end
+
+  scenario 'Changing the locale', :js do
+    visit '/'
+    expect(page).to have_content('Site language')
+
+    select('Español', from: 'locale-switcher')
+    expect(page).to have_content('Idioma de la página')
+    expect(page).to_not have_content('Site language')
+    expect(page).to have_select('locale-switcher', selected: 'Español')
+  end
+
+end