Add as_id_list helper for tests

Signed-off-by: Roberto Rosario <Roberto.Rosario@mayan-edms.com>

mayan/apps/common/tests/utils.py

@@ -1,12 +1,22 @@
+from __future__ import absolute_import, unicode_literals
+
 from contextlib import contextmanager
 import sys
 
+from django.utils.encoding import force_text
+
 
 class NullFile(object):
     def write(self, string):
         """Writes here go nowhere"""
 
 
+def as_id_list(items):
+    return ','.join(
+        [force_text(item.pk) for item in items]
+    )
+
+
 @contextmanager
 def mute_stdout():
     stdout_old = sys.stdout