check if username is available in registration form

spec/features/registration_form_spec.rb

@@ -0,0 +1,27 @@
+require 'rails_helper'
+
+feature 'Registration form' do
+
+  scenario 'username is not available', :js do
+    user = create(:user)
+
+    visit new_user_registration_path
+    expect(page).to_not have_content I18n.t("devise_views.users.registrations.new.username_is_not_available")
+
+    fill_in "user_username", with: user.username
+    check 'user_terms_of_service'
+
+    expect(page).to have_content I18n.t("devise_views.users.registrations.new.username_is_not_available")
+  end
+
+  scenario 'username is available', :js do
+    visit new_user_registration_path
+    expect(page).to_not have_content I18n.t("devise_views.users.registrations.new.username_is_available")
+
+    fill_in "user_username", with: "available username"
+    check 'user_terms_of_service'
+
+    expect(page).to have_content I18n.t("devise_views.users.registrations.new.username_is_available")
+  end
+
+end