Add test mixin to generate random primary keys

Add a new mixin to monkey patch the Model class to
force each newly created model instance to use a randomly
generated primary key.

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

HISTORY.rst

@@ -224,6 +224,7 @@
   of the permission proxy support which is now redundant.
 - Remove the permissions to grant or revoke a permission to a role.
   The instead the role edit permission is used.
+- Add a test mixin to generate random model primary keys.
 
 3.1.9 (2018-11-01)
 ==================

mayan/apps/common/tests/base.py

@@ -1,7 +1,6 @@
 from __future__ import absolute_import, unicode_literals
 
 from django.test import TestCase
-from django.urls import reverse
 from django_downloadview import assert_download_response
 
 from mayan.apps.acls.tests.mixins import ACLTestCaseMixin
@@ -10,12 +9,12 @@ from mayan.apps.smart_settings.classes import Namespace
 
 from .mixins import (
     ClientMethodsTestCaseMixin, ContentTypeCheckMixin, DatabaseConversionMixin,
-    OpenFileCheckTestCaseMixin, TempfileCheckTestCaseMixin,
-    TestViewTestCaseMixin
+    OpenFileCheckTestCaseMixin, RandomPrimaryKeyModelMonkeyPatchMixin,
+    TempfileCheckTestCaseMixin, TestViewTestCaseMixin
 )
 
 
-class BaseTestCase(DatabaseConversionMixin, ACLTestCaseMixin, ContentTypeCheckMixin, OpenFileCheckTestCaseMixin, TempfileCheckTestCaseMixin, TestCase):
+class BaseTestCase(RandomPrimaryKeyModelMonkeyPatchMixin, DatabaseConversionMixin, ACLTestCaseMixin, ContentTypeCheckMixin, OpenFileCheckTestCaseMixin, TempfileCheckTestCaseMixin, TestCase):
     """
     This is the most basic test case class any test in the project should use.
     """

mayan/apps/common/tests/mixins.py

@@ -2,10 +2,12 @@ from __future__ import unicode_literals
 
 import glob
 import os
+import random
 
 from django.conf import settings
 from django.conf.urls import url
 from django.core import management
+from django.db import models
 from django.http import HttpResponse
 from django.template import Context, Template
 from django.test.utils import ContextList
@@ -138,6 +140,53 @@ class OpenFileCheckTestCaseMixin(object):
         super(OpenFileCheckTestCaseMixin, self).tearDown()
 
 
+class RandomPrimaryKeyModelMonkeyPatchMixin(object):
+    random_primary_key_random_floor = 100
+    random_primary_key_random_ceiling = 10000
+    random_primary_key_maximum_attempts = 100
+
+    @staticmethod
+    def get_unique_primary_key(model):
+        pk_list = model._meta.default_manager.values_list('pk', flat=True)
+
+        attempts = 0
+        while True:
+            primary_key = random.randint(
+                RandomPrimaryKeyModelMonkeyPatchMixin.random_primary_key_random_floor,
+                RandomPrimaryKeyModelMonkeyPatchMixin.random_primary_key_random_ceiling
+            )
+
+            if primary_key not in pk_list:
+                break
+
+            attempts = attempts + 1
+
+            if attempts > RandomPrimaryKeyModelMonkeyPatchMixin.random_primary_key_maximum_attempts:
+                raise Exception(
+                    'Maximum number of retries for an unique random primary '
+                    'key reached.'
+                )
+
+        return primary_key
+
+    def setUp(self):
+        original_save = models.Model.save
+
+        def new_save(self, *args, **kwargs):
+            if self.pk:
+                return original_save(self, *args, **kwargs)
+            else:
+                self.pk = RandomPrimaryKeyModelMonkeyPatchMixin.get_unique_primary_key(
+                    model=self._meta.model
+                )
+                self.id = self.pk
+
+                return self.save_base(force_insert=True)
+
+        setattr(models.Model, 'save', new_save)
+        super(RandomPrimaryKeyModelMonkeyPatchMixin, self).setUp()
+
+
 class TempfileCheckTestCaseMixin(object):
     # Ignore the jvmstat instrumentation and GitLab's CI .config files
     # Ignore LibreOffice fontconfig cache dir