Proactively specify aws region for s3 operations

tests/app/aws/test_s3.py

@@ -1,11 +1,16 @@
-import os
 from datetime import datetime, timedelta
 
 import pytest
 import pytz
 from freezegun import freeze_time
 
-from app.aws.s3 import get_list_of_files_by_suffix, get_s3_file
+from app.aws.s3 import (
+    default_access_key,
+    default_region,
+    default_secret_key,
+    get_list_of_files_by_suffix,
+    get_s3_file,
+)
 from tests.app.conftest import datetime_in_past
 
 
@@ -24,8 +29,9 @@ def test_get_s3_file_makes_correct_call(notify_api, mocker):
     get_s3_mock.assert_called_with(
         'foo-bucket',
         'bar-file.txt',
-        os.environ['AWS_ACCESS_KEY_ID'],
-        os.environ['AWS_SECRET_ACCESS_KEY']
+        default_access_key,
+        default_secret_key,
+        default_region,
     )