tests: add a testcase for user collision

test/web/activity_pub/transmogrifier_test.exs

@@ -955,5 +955,17 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
           data
         )
     end
+
+    test "users cannot be collided through fake direction spoofing attempts" do
+      user =
+        insert(:user, %{
+          nickname: "rye@niu.moe",
+          local: false,
+          ap_id: "https://niu.moe/users/rye",
+          follower_address: User.ap_followers(%User{nickname: "rye@niu.moe"})
+        })
+
+      {:error, _} = User.get_or_fetch_by_ap_id("https://n1u.moe/users/rye")
+    end
   end
 end