Notifications testing - best practices

[mkasztelnik]

At the beginning many thanks for the great library :)

I'm in the process of transitioning from the pure mail sending to notifications. In the beginning, I want to incrementally convert mail.deliver_later to MyNotification.deliver_later. The notifications will have only deliver_by :email declaration (no deliver_by :database). After all emails are changed to the notifications more advanced delivery methods will be added.

I was struggling with testing the new notifications approach in my application. I added this simple assertion to my application in order to check if the user is notified by the email:

module Noticed
  module TestHelper
    include ActiveJob::TestHelper

    def assert_notified_by_email(mailer:, method:, params: nil, recipients: nil, &block)
      original_performed_jobs_count = performed_jobs.count

      perform_enqueued_jobs(&block)

      in_block_jobs = performed_jobs.drop(original_performed_jobs_count)
      matching_job = in_block_jobs.find do |in_block_job|
        deserialized_job = deserialize_args_for_assertion(in_block_job)
        args = deserialized_job[:args]&.first

        deserialized_job[:job] == Noticed::DeliveryMethods::Email &&
          args.dig(:options, :mailer) == mailer &&
          args.dig(:options, :method) == method &&
          (params || {}).all? { |key, value| value == args.dig(:params, key) } &&
          (recipients || []).any? { |recipient| recipient == args.dig(:recipient) }
      end
      assert matching_job, "No email notification sent with params... #{{ mailer:, method:, params:, recipients: }}"
      instantiate_job(matching_job)
    end
  end
end

but it seems to me like testing the application on the wrong abstraction level (I'm testing here no notification itself but the delivery method, which is a notification implementation detail).

Do you have any other recommendations/best practices on how to test notifications (without testing record creation in the DB, because the situation is similar to my assert_notified_by_email case)?

Notification testing like the active job?

I was also thinking about the similarity between notified and active job. Maybe the library can be extended with the backend support, which in the test environment can add notifications to the collection without DB record creation, triggering additional delayed jobs?

assert_notified_with notifier: MyNotification, params: { foo: 1, bar: "asdf" } do
  application.logic
end

Do you think this is something worth adding to the library?