revert stubber and add session test

tests/functional/test_credentials.py

@@ -790,9 +790,7 @@ def assert_session_credentials(self, expected_params, **kwargs):
         expected_creds = self.create_random_credentials()
         response = self.create_assume_role_response(expected_creds)
         session = StubbedSession(**kwargs)
-        stubber = session.stub(
-            'sts', config=Config(signature_version=UNSIGNED)
-        )
+        stubber = session.stub('sts')
         stubber.add_response(
             'assume_role_with_web_identity', response, expected_params
         )

tests/unit/test_session.py

@@ -549,6 +549,20 @@ def test_cred_provider_called_when_partial_creds_provided(self):
                 aws_secret_access_key='foo',
             )
 
+    @mock.patch('botocore.client.ClientCreator')
+    def test_account_id(self, client_creator):
+        self.session.create_client(
+            'sts',
+            'us-west-2',
+            aws_access_key_id='foo',
+            aws_secret_access_key='bar',
+            aws_session_token='baz',
+            aws_account_id='123456789012',
+        )
+        call_args = client_creator.return_value.create_client.call_args[1]
+        credentials = call_args['credentials']
+        self.assertEqual(credentials.account_id, '123456789012')
+
     def test_cred_provider_not_called_on_unsigned_client(self):
         cred_provider = mock.Mock()
         self.session.register_component('credential_provider', cred_provider)