Enforce randomness on unspecified value of scheduled task

Closes #13484

trytond/trytond/ir/cron.py

@@ -3,6 +3,7 @@
 import datetime
 import hashlib
 import logging
+import random
 import time
 from collections import defaultdict
 
@@ -181,15 +182,18 @@ class Cron(DeactivableMixin, ModelSQL, ModelView):
                 microsecond=0,
                 second=0,
                 minute=(
-                    self.minute
+                    (self.minute if self.minute is not None
+                        else random.randint(0, 59))
                     if self.interval_type != 'minutes'
                     else None),
                 hour=(
-                    self.hour
+                    (self.hour if self.hour is not None
+                        else random.randint(0, 23))
                     if self.interval_type not in {'minutes', 'hours'}
                     else None),
                 day=(
-                    self.day
+                    (self.day if self.day is not None
+                        else random.randint(0, 31))
                     if self.interval_type not in {
                         'minutes', 'hours', 'days', 'weeks'}
                     else None),

trytond/trytond/tests/test_ir.py

@@ -515,6 +515,7 @@ class IrCronTestCase(TestCase):
         cron.interval_number = 1
         cron.interval_type = 'days'
         cron.hour = 1
+        cron.minute = 0
 
         # Quebec is UTC-5
         self.assertEqual(
@@ -529,6 +530,7 @@ class IrCronTestCase(TestCase):
         cron.interval_number = 1
         cron.interval_type = 'days'
         cron.hour = 2
+        cron.minute = 30
 
         # 2022-03-13 is the day of DST switch
         # Quebec is UTC-4
@@ -542,6 +544,7 @@ class IrCronTestCase(TestCase):
         cron = self._get_cron()
         cron.interval_number = 1
         cron.interval_type = 'hours'
+        cron.minute = 30
 
         # 2022-11-06 is the day of DST switch
         # Quebec is UTC-5