test: add ActionMailer callbacks idempotency test to bump coverage

Author: ndbroadbent

test/integrations/action_mailer_callbacks_idempotent_test.rb

@@ -0,0 +1,12 @@
+# typed: true
+# frozen_string_literal: true
+
+require "test_helper"
+
+class ActionMailerCallbacksIdempotentTest < ActiveSupport::TestCase
+  test "patch_message_delivery is idempotent" do
+    assert LogStruct::Integrations::ActionMailer::Callbacks.patch_message_delivery
+    # Calling again should be a no-op and still return true
+    assert LogStruct::Integrations::ActionMailer::Callbacks.patch_message_delivery
+  end
+end