fix test server error

moto/sqs/responses.py

@@ -406,7 +406,11 @@ class SQSResponse(BaseResponse):
         queue_name = self._get_queue_name()
         tag_keys = self._get_multi_param('TagKey')
 
-        self.sqs_backend.untag_queue(queue_name, tag_keys)
+        try:
+            self.sqs_backend.untag_queue(queue_name, tag_keys)
+        except QueueDoesNotExist as e:
+            return self._error('AWS.SimpleQueueService.NonExistentQueue',
+                               e.description)
 
         template = self.response_template(UNTAG_QUEUE_RESPONSE)
         return template.render()

tests/test_sqs/test_sqs.py

@@ -17,7 +17,6 @@ import time
 import uuid
 
 from moto import settings, mock_sqs, mock_sqs_deprecated
-from moto.sqs.exceptions import QueueDoesNotExist
 from tests.helpers import requires_boto_gte
 import tests.backport_assert_raises  # noqa
 from nose.tools import assert_raises
@@ -1006,7 +1005,8 @@ def test_untag_queue_errors():
             'tag_key_1'
         ]
     ).should.throw(
-        QueueDoesNotExist
+        ClientError,
+        "The specified queue does not exist for this wsdl version."
     )
 
     client.untag_queue.when.called_with(