Add test for broken owncast federation

test/fixtures/owncast-note-with-attachment.json

@@ -0,0 +1,31 @@
+{
+  "attachment": {
+    "content": "Live stream preview",
+    "type": "Image",
+    "url": "https://owncast.localhost.localdomain/preview.gif?us=KjfNX387gm"
+  },
+  "attributedTo": "https://owncast.localhost.localdomain/federation/user/streamer",
+  "audience": "https://www.w3.org/ns/activitystreams#Public",
+  "content": "<p>I've gone live!</p><p></p><p><a class=\"hashtag\" href=\"https://directory.owncast.online/tags/owncast\">#owncast</a> <a class=\"hashtag\" href=\"https://directory.owncast.online/tags/streaming\">#streaming</a></p><a href=\"https://owncast.localhost.localdomain\">https://owncast.localhost.localdomain</a>",
+  "id": "https://owncast.localhost.localdomain/federation/KjBNuq8ng",
+  "published": "2022-04-17T15:42:03Z",
+  "tag": [
+    {
+      "href": "https://directory.owncast.online/tags/owncast",
+      "name": "#owncast",
+      "type": "Hashtag"
+    },
+    {
+      "href": "https://directory.owncast.online/tags/streaming",
+      "name": "#streaming",
+      "type": "Hashtag"
+    },
+    {
+      "href": "https://directory.owncast.online/tags/owncast",
+      "name": "#owncast",
+      "type": "Hashtag"
+    }
+  ],
+  "to": "https://www.w3.org/ns/activitystreams#Public",
+  "type": "Note"
+}

test/pleroma/web/activity_pub/object_validators/article_note_page_validator_test.exs

@@ -43,4 +43,15 @@ defmodule Pleroma.Web.ActivityPub.ObjectValidators.ArticleNotePageValidatorTest
 
     %{valid?: true} = ArticleNotePageValidator.cast_and_validate(note)
   end
+
+  test "a note with an attachment should work", _ do
+    insert(:user, %{ap_id: "https://owncast.localhost.localdomain/federation/user/streamer"})
+
+    note =
+      "test/fixtures/owncast-note-with-attachment.json"
+      |> File.read!()
+      |> Jason.decode!()
+
+    %{valid?: true} = ArticleNotePageValidator.cast_and_validate(note)
+  end
 end