bpo-39481: Make weakref and WeakSet generic (GH-19497)

diff --git a/Lib/test/test_genericalias.py b/Lib/test/test_genericalias.py
index 770aeef..686df17 100644
--- a/Lib/test/test_genericalias.py
+++ b/Lib/test/test_genericalias.py
@@ -33,6 +33,7 @@
 from urllib.parse import SplitResult, ParseResult
 from unittest.case import _AssertRaisesContext
 from queue import Queue, SimpleQueue
+from weakref import WeakSet, ReferenceType, ref
 import typing
 
 from typing import TypeVar
@@ -73,6 +74,7 @@
                   Array, LibraryLoader,
                   SplitResult, ParseResult,
                   ValueProxy, ApplyResult,
+                  WeakSet, ReferenceType, ref,
                   ShareableList, SimpleQueue,
                   Future, _WorkItem,
                   Morsel,