add further locale tests

test/mv_web/locale_test.exs

@@ -0,0 +1,14 @@
+defmodule MvWeb.LocaleTest do
+  use MvWeb.ConnCase, async: true
+  import Phoenix.ConnTest
+
+  test "language switch via form sets the locale to English in the session" do
+    conn = post(build_conn(), "/set_locale", %{"locale" => "en"})
+    assert get_session(conn, :locale) == "en"
+  end
+
+  test "language switch via form sets the locale to German in the session" do
+    conn = post(build_conn(), "/set_locale", %{"locale" => "de"})
+    assert get_session(conn, :locale) == "de"
+  end
+end