tests: disable boto3 session caching to fix moto issues

If instances of clients are created outside of the moto patching, they
will be cached by boto3 and return in subsequent runs, breaking some
tests. While the best fix would be to avoid that situation, disabling
the caching altogether is easier and ensures the issue won't return.

Author: danielkza

stacker/tests/conftest.py

@@ -2,8 +2,10 @@
 
 import logging
 import os
+import mock
 
 import pytest
+from boto3 import Session
 
 
 logger = logging.getLogger(__name__)
@@ -35,3 +37,13 @@ def aws_credentials():
             os.environ[key] = value
 
     saved_env.clear()
+
+
+@pytest.fixture(scope='session', autouse=True)
+def boto3_disable_session_caching():
+    def get_session(**kwargs):
+        return Session(**kwargs)
+
+    with mock.patch('boto3._get_default_session',
+                    side_effect=get_session):
+        yield