How do I test that my Category resource is sending notifications?

Here my resource definition

defmodule MyApp.KnowledgeBase.Category do
  use Ash.Resource,
    domain: Helpcenter.KnowledgeBase,
    data_layer: AshPostgres.DataLayer,
    # Tell Ash to broadcast/ Emit events via pubsub
    notifiers: Ash.Notifier.PubSub
    
  pub_sub do
    module HelpcenterWeb.Endpoint

    prefix "categories"

    publish_all :update, [[:id, nil]]
    publish_all :create, [[:id, nil]]
    publish_all :destroy, [[:id, nil]]
  end
end

Here is the test:

test "'categories'  event should be published on create" do
      Helpcenter.KnowledgeBase.Category
      |> Ash.Changeset.for_create(:create, %{
        name: "Art 1",
        slug: "art-1",
        description: "descrpt-1"
      })
      |> Ash.create()

      assert_receive {:broadcast, "categories", "create", %Ash.Notifier.Notification{}}
    end

The above tests returns:

     Assertion failed, no matching message after 100ms
     The process mailbox is empty.