Add some basic changesets.

test/object_test.exs

@@ -1,11 +1,22 @@
 defmodule Pleroma.ObjectTest do
   use Pleroma.DataCase
   import Pleroma.Factory
+  alias Pleroma.{Repo, Object}
 
   test "returns an object by it's AP id" do
     object = insert(:note)
-    found_object = Pleroma.Object.get_by_ap_id(object.data["id"])
+    found_object = Object.get_by_ap_id(object.data["id"])
 
     assert object == found_object
   end
+
+  describe "generic changeset" do
+    test "it ensures uniqueness of the id" do
+      object = insert(:note)
+      cs = Object.change(%Object{}, %{data: %{id: object.data["id"]}})
+      assert cs.valid?
+
+      {:error, result} = Repo.insert(cs)
+    end
+  end
 end