def METHOD_NAME(invite_to_slack, client, organizer_peter, future_event, hidden_event):
    add_organizers_url = reverse("admin:core_event_add_organizers")
    client.force_login(organizer_peter)
    data = {"event": hidden_event.pk, "name": "New organizer", "email": "new@organizer.com"}
    # Mock call to slack
    resp = client.post(add_organizers_url, data)
    assert resp.status_code == 200
    assert len(resp.context["form"].errors) == 1
    data = {"event": future_event.pk, "name": "New organizer", "email": "new@organizer.com"}
    resp = client.post(add_organizers_url, data)
    assert resp.status_code == 302