add integration specs for changing locales

app/controllers/application_controller.rb

@@ -11,9 +11,7 @@ class ApplicationController < ActionController::Base
   before_action :find_active_announcements
 
   # check if user wants to read
-  def switch_locale(&) # rubocop:disable Metrics/AbcSize, Metrics/CyclomaticComplexity
-    return I18n.with_locale("en", &) if Rails.env.test?
-
+  def switch_locale(&)
     locale = params[:lang] || current_user&.locale || cookies[:lang] || "en"
     if params[:lang] && current_user.present?
       current_user.locale = locale

spec/integration/locale_switch_spec.rb

@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+require "nokogiri"
+
+describe "locale switching", type: :request do
+  matcher :have_html_lang do |expected_lang|
+    description { %(have the HTML "lang" attribute set to #{expected_lang.inspect}) }
+
+    match do |result|
+      Nokogiri::HTML.parse(result).css("html[lang=#{expected_lang}]").size == 1
+    end
+  end
+
+  context "when user not signed in" do
+    it "uses the default :en locale" do
+      get "/"
+      expect(response.body).to have_html_lang "en"
+      expect(response.cookies["lang"]).to eq "en"
+    end
+
+    context "when ?lang param is given" do
+      it "changes the locale" do
+        # 1. ensure we start with the default :en locale
+        get "/"
+        expect(response.body).to have_html_lang "en"
+        expect(response.cookies["lang"]).to eq "en"
+
+        # 2. switch the language to en-xx
+        get "/?lang=en-xx"
+        expect(response.body).to have_html_lang "en-xx"
+        expect(response.cookies["lang"]).to eq "en-xx"
+
+        # 3. remove the language parameter again
+        get "/"
+        expect(response.body).to have_html_lang "en-xx"
+        expect(response.cookies["lang"]).to be_nil # no new cookie here, it's already en-xx
+      end
+    end
+  end
+
+  context "when user is signed in" do
+    let(:user) { FactoryBot.create(:user, password: "test1234", locale:) }
+    let(:locale) { "en" }
+
+    before do
+      post "/sign_in", params: { user: { login: user.email, password: user.password } }
+    end
+
+    it "uses the en locale" do
+      get "/"
+      expect(response.body).to have_html_lang "en"
+      expect(response.cookies["lang"]).to be_nil # no new cookie here, already set by the sign in
+    end
+
+    context "when ?lang param is given" do
+      it "changes the locale" do
+        # 1. ensure we start with the :en locale
+        get "/"
+        expect(response.body).to have_html_lang "en"
+        expect(response.cookies["lang"]).to be_nil # no new cookie here, already set by the sign in
+
+        # 2. switch the language to en-xx
+        expect { get "/?lang=en-xx" }.to change { user.reload.locale }.from("en").to("en-xx")
+        expect(response.body).to have_html_lang "en-xx"
+        expect(response.cookies["lang"]).to eq "en-xx"
+
+        # 3. remove the language parameter again
+        get "/"
+        expect(response.body).to have_html_lang "en-xx"
+        expect(response.cookies["lang"]).to be_nil # no new cookie here, it's already en-xx
+      end
+    end
+
+    context "when user has a different locale set" do
+      let(:locale) { "fi" }
+
+      it "uses the different locale" do
+        get "/"
+        expect(response.body).to have_html_lang "fi"
+        expect(response.cookies["lang"]).to be_nil # no new cookie here, already set by the sign in
+      end
+    end
+  end
+end