|  | @@ -3825,7 +3825,8 @@ class SerializeTest(unittest.TestCase):
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				|  |  |          }
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				|  |  |          secrets_dict = {
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				|  |  |              'one': {'file': '/one.txt'},
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				|  |  | -            'source': {'file': '/source.pem'}
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				|  |  | +            'source': {'file': '/source.pem'},
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				|  |  | +            'two': {'external': True},
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				|  |  |          }
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				|  |  |          config_dict = config.load(build_config_details({
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				|  |  |              'version': '3.1',
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				|  | @@ -3837,6 +3838,7 @@ class SerializeTest(unittest.TestCase):
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				|  |  |          serialized_service = serialized_config['services']['web']
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				|  |  |          assert secret_sort(serialized_service['secrets']) == secret_sort(service_dict['secrets'])
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				|  |  |          assert 'secrets' in serialized_config
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				|  |  | +        assert serialized_config['secrets']['two'] == secrets_dict['two']
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				|  |  |  
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				|  |  |      def test_serialize_ports(self):
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				|  |  |          config_dict = config.Config(version='2.0', services=[
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