test: add tests for join request page

test/mv_web/controllers/join_confirm_controller_test.exs

@@ -60,13 +60,18 @@ defmodule MvWeb.JoinConfirmControllerTest do
     end
 
     @tag role: :unauthenticated
-    test "expired token returns 200 with expired message", %{conn: conn} do
+    test "expired token returns 200 with expired message and instructs to submit form again", %{
+      conn: conn
+    } do
       Application.put_env(:mv, :join_confirm_callback, JoinConfirmExpiredStub)
 
       conn = get(conn, "/confirm_join/expired-token")
+      body = response(conn, 200)
 
-      assert response(conn, 200) =~ "expired"
-      assert response(conn, 200) =~ "submit"
+      assert body =~ "expired"
+      assert body =~ "submit"
+      # Concept §2.5: clear message + "submit form again"
+      assert body =~ "form" or body =~ "again"
     end
 
     @tag role: :unauthenticated