Use YAML SafeDumper to avoid adding YAML tags

Closes GitLab issue #599. Thanks to Frédéric Sheedy
(@fsheedy) for the report and debug information.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

mayan/apps/smart_settings/tests/test_classes.py

@@ -2,9 +2,15 @@ from __future__ import absolute_import, unicode_literals
 
 import os
 
+from pathlib2 import Path
+
+from django.conf import settings
+
 from mayan.apps.common.settings import setting_paginate_by
 from mayan.apps.common.tests import BaseTestCase
 
+from ..classes import Setting
+
 from .literals import ENVIRONMENT_TEST_NAME, ENVIRONMENT_TEST_VALUE
 
 
@@ -14,3 +20,20 @@ class ClassesTestCase(BaseTestCase):
             'MAYAN_{}'.format(ENVIRONMENT_TEST_NAME)
         ] = ENVIRONMENT_TEST_VALUE
         self.assertTrue(setting_paginate_by.value, ENVIRONMENT_TEST_VALUE)
+
+    def test_config_backup_creation(self):
+        path_config_backup = Path(settings.CONFIGURATION_LAST_GOOD_FILEPATH)
+        path_config_backup.unlink()
+
+        Setting.save_last_known_good()
+        self.assertTrue(path_config_backup.exists())
+
+    def test_config_backup_creation_no_tags(self):
+        path_config_backup = Path(settings.CONFIGURATION_LAST_GOOD_FILEPATH)
+        path_config_backup.unlink()
+
+        Setting.save_last_known_good()
+        self.assertTrue(path_config_backup.exists())
+
+        with path_config_backup.open(mode='r') as file_object:
+            self.assertFalse('!!python/' in file_object.read())