test: add tests for smtp mailer config

test/mv_web/live/join_live_test.exs

@@ -39,6 +39,8 @@ defmodule MvWeb.JoinLiveTest do
     test "submit with valid allowlist data creates one JoinRequest and shows success copy", %{
       conn: conn
     } do
+      # Re-apply allowlist so this test is robust when run in parallel with others (Settings singleton).
+      enable_join_form_for_test(%{})
       count_before = count_join_requests()
       {:ok, view, _html} = live(conn, "/join")