gh-156460: Await async callable side effects in AsyncMock

Lib/test/test_unittest/testmock/testasync.py

@@ -468,6 +468,24 @@ async def addition(var):
         result = await mock(5)
         self.assertEqual(result, 6)
 
+    async def test_add_side_effect_async_callable(self):
+        class AsyncCallable:
+            async def __call__(self, var):
+                return var + 1
+
+        mock = AsyncMock(side_effect=AsyncCallable())
+        result = await mock(5)
+        self.assertEqual(result, 6)
+
+    async def test_add_side_effect_sync_callable(self):
+        class SyncCallable:
+            def __call__(self, var):
+                return var + 1
+
+        mock = AsyncMock(side_effect=SyncCallable())
+        result = await mock(5)
+        self.assertEqual(result, 6)
+
     async def test_add_side_effect_normal_function(self):
         def addition(var):
             return var + 1

Lib/unittest/mock.py

@@ -2331,7 +2331,8 @@ async def _execute_mock_call(self, /, *args, **kwargs):
                     raise StopAsyncIteration
                 if _is_exception(result):
                     raise result
-            elif iscoroutinefunction(effect):
+            elif (iscoroutinefunction(effect) or
+                  iscoroutinefunction(getattr(effect, '__call__', None))):
                 result = await effect(*args, **kwargs)
             else:
                 result = effect(*args, **kwargs)

Misc/NEWS.d/next/Library/2026-08-27-20-47-01.gh-issue-156460.A7kP3m.rst

@@ -0,0 +1,2 @@
+Correctly handle async callable objects used as the ``side_effect`` of
+:class:`unittest.mock.AsyncMock`.