[V3 DataConverter] Fix past nicks conversion for mod (#1840)

* Fix existing tests permanently modifying attributes

* Add dataconverter tests file

* Fix past nicks spec converter

* Update gitignore for dataconverter data files

* Add data file for dataconverter test

* Simplify fix

tests/cogs/dataconverter/test_dataconverter.py

@@ -0,0 +1,39 @@
+import pytest
+from pathlib import Path
+from collections import namedtuple
+
+from redbot.cogs.dataconverter import core_specs
+from redbot.core.utils.data_converter import DataConverter
+
+
+def mock_dpy_object(id_):
+    return namedtuple("DPYObject", "id")(int(id_))
+
+
+def mock_dpy_member(guildid, userid):
+    return namedtuple("Member", "id guild")(int(userid), mock_dpy_object(guildid))
+
+
+@pytest.fixture()
+def specresolver():
+    here = Path(__file__)
+
+    resolver = core_specs.SpecResolver(here.parent)
+    return resolver
+
+
+@pytest.mark.asyncio
+async def test_mod_nicknames(red, specresolver: core_specs.SpecResolver):
+    filepath, converter, cogname, attr, _id = specresolver.get_conversion_info("Past Nicknames")
+    conf = specresolver.get_config_object(red, cogname, attr, _id)
+
+    v2data = DataConverter.json_load(filepath)
+
+    await specresolver.convert(red, "Past Nicknames", config=conf)
+
+    for guildid, guild_data in v2data.items():
+        guild = mock_dpy_object(guildid)
+        for userid, user_data in guild_data.items():
+            member = mock_dpy_member(guildid, userid)
+
+            assert await conf.member(member).past_nicks() == user_data