def METHOD_NAME(self, mock_boto3):
    error = ClientError({'Error': {'Code': '403',
                                   'Message': 'Permission denied'}},
                        'error')
    mock_boto3.Session().resource().Object().load.side_effect = error
    self.app.conf.s3_access_key_id = 'somekeyid'
    self.app.conf.s3_secret_access_key = 'somesecret'
    self.app.conf.s3_bucket = 'bucket'
    s3_backend = S3Backend(app=self.app)
    with pytest.raises(ClientError):
        s3_backend.get('uuidddd')