add pytest decorator for skipping py3 test (#21151)

* add pytest decorator for skipping py3 test

* quality

common/test/utils.py

@@ -6,6 +6,7 @@ import sys
 from contextlib import contextmanager
 
 import moto
+import pytest
 from django.dispatch import Signal
 from markupsafe import escape
 from mock import Mock, patch
@@ -153,3 +154,13 @@ def normalize_repr(func):
     between worker processes.
     """
     return reprwrapper(func)
+
+
+# Decorator for skipping tests that are not ready to be run with Python 3.x.
+# While we expect many tests to fail with Python 3.x as we transition, this
+# is specifically for tests that rely on external or large scale fixes. It can
+# be added to individual tests or test classes.
+py2_only = pytest.mark.skipif(
+    sys.version_info > (3, 0),
+    reason="This test can only be run with Python 2.7, currently"
+)