Make random PK mixin work with pre_save signals

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

mayan/apps/common/tests/mixins.py

@@ -11,8 +11,8 @@ from django.conf import settings
 from django.conf.urls import url
 from django.contrib.contenttypes.models import ContentType
 from django.core import management
-from django.db import connection
-from django.db import models
+from django.db import connection. models
+from django.db.models.signals import post_save, pre_save
 from django.http import HttpResponse
 from django.template import Context, Template
 from django.test.utils import ContextList
@@ -176,12 +176,35 @@ class RandomPrimaryKeyModelMonkeyPatchMixin(object):
             if instance.pk:
                 return self.method_save_original(instance, *args, **kwargs)
             else:
+                # Set meta.auto_created to True to have the original save_base
+                # not send the pre_save signal which would normally send
+                # the instance without a primary key. Since we assign a random
+                # primary key any pre_save signal handler that relies on an 
+                # empty primary key will fail.
+                # The meta.auto_created and manual pre_save sending emulates
+                # the original behavior. Since meta.auto_created also disables
+                # the post_save signal we must also send it ourselves.
+                # This hack work with Django 1.11 .save_base() but can break
+                # in future versions if that method is updated.
+                pre_save.send(
+                    sender=instance.__class__, instance=instance, raw=False,
+                    update_fields=None,
+                )
+                instance._meta.auto_created = True
                 instance.pk = RandomPrimaryKeyModelMonkeyPatchMixin.get_unique_primary_key(
                     model=instance._meta.model
                 )
                 instance.id = instance.pk
 
-                return instance.save_base(force_insert=True)
+                result = instance.save_base(force_insert=True)
+                instance._meta.auto_created = False
+                
+                post_save.send(
+                    sender=instance.__class__, instance=instance, created=True,
+                    update_fields=None, raw=False
+                )
+
+                return result
 
         setattr(models.Model, 'save', method_save_new)
         super(RandomPrimaryKeyModelMonkeyPatchMixin, self).setUp()