test: Convert test_registry.py from unittest to pytest

tests/unittests/test_registry.py

@@ -1,30 +1,31 @@
 # This file is part of cloud-init. See LICENSE file for license information.
 
+from unittest import mock
+
+import pytest
+
 from cloudinit.registry import DictRegistry
-from tests.unittests.helpers import TestCase, mock
 
 
-class TestDictRegistry(TestCase):
+class TestDictRegistry:
     def test_added_item_included_in_output(self):
         registry = DictRegistry()
         item_key, item_to_register = "test_key", mock.Mock()
         registry.register_item(item_key, item_to_register)
-        self.assertEqual(
-            {item_key: item_to_register}, registry.registered_items
-        )
+        assert {item_key: item_to_register} == registry.registered_items
 
     def test_registry_starts_out_empty(self):
-        self.assertEqual({}, DictRegistry().registered_items)
+        assert {} == DictRegistry().registered_items
 
     def test_modifying_registered_items_isnt_exposed_to_other_callers(self):
         registry = DictRegistry()
         registry.registered_items["test_item"] = mock.Mock()
-        self.assertEqual({}, registry.registered_items)
+        assert {} == registry.registered_items
 
     def test_keys_cannot_be_replaced(self):
         registry = DictRegistry()
         item_key = "test_key"
         registry.register_item(item_key, mock.Mock())
-        self.assertRaises(
-            ValueError, registry.register_item, item_key, mock.Mock()
-        )
+
+        with pytest.raises(ValueError):
+            registry.register_item(item_key, mock.Mock())