Use stdlib AsyncMock when available (#1297)

test-requirements.txt

@@ -10,7 +10,7 @@ anyio[trio] == 3.6.2
 
 pytest-cov >= 2.8.1, < 2.11.0
 pytest-mock >= 2.0.0
-asyncmock >= 0.4.2
+mock >= 4.0; python_version < "3.8"
 pytest-xdist >= 1.31.0
 pytest >= 6.0.0
 coverage >= 4.5.3, < 5

tests/test_http_client.py

@@ -3,7 +3,12 @@
 from unittest.mock import call
 import pytest
 import json
-from mock import AsyncMock
+import sys
+
+if sys.version_info >= (3, 8):
+    from unittest.mock import AsyncMock
+else:
+    from mock import AsyncMock
 
 import stripe
 from stripe import _http_client