More robust test for the _partialmethod attribute.

The asyncio tests pass in a mock.Mock() instance and it always has
any attribute, so the test enters an infinite loop. This change
avoids that trap.

Author: mjpieters

Lib/functools.py

@@ -417,8 +417,8 @@ def _unwrap_partialmethod(func):
     prev = None
     while func is not prev:
         prev = func
-        while hasattr(func, "_partialmethod"):
-            func = getattr(func, '_partialmethod')
+        while isinstance(getattr(func, "_partialmethod", None), partialmethod):
+            func = func._partialmethod
         while isinstance(func, partialmethod):
             func = getattr(func, 'func')
         func = _unwrap_partial(func)