Fix intermittent unit test failures (#20783)

openedx/core/djangoapps/schedules/management/commands/tests/send_email_base.py

@@ -12,6 +12,8 @@ import attr
 import ddt
 import pytz
 from django.conf import settings
+from django.contrib.auth.models import User
+from django.db.models import Max
 from edx_ace.channel import ChannelMap, ChannelType
 from edx_ace.test_utils import StubPolicy, patch_policies
 from edx_ace.utils.date import serialize
@@ -105,6 +107,18 @@ class ScheduleSendEmailTestMixin(FilteredQueryCountMixin):
     def _calculate_bin_for_user(self, user):
         return user.id % self.task.num_bins
 
+    def _next_user_id(self):
+        """
+        Get the next user ID which is a multiple of the bin count and greater
+        than the current largest user ID.  Avoids intermittent ID collisions
+        with the user created in ModuleStoreTestCase.setUp().
+        """
+        max_user_id = User.objects.aggregate(Max('id'))['id__max']
+        if max_user_id is None:
+            max_user_id = 0
+        num_bins = self.task.num_bins
+        return max_user_id + num_bins - (max_user_id % num_bins)
+
     def _get_dates(self, offset=None):
         current_day = _get_datetime_beginning_of_day(datetime.datetime.now(pytz.UTC))
         offset = offset or self.expected_offsets[0]
@@ -296,8 +310,8 @@ class ScheduleSendEmailTestMixin(FilteredQueryCountMixin):
         for config in (this_config, other_config):
             ScheduleConfigFactory.create(site=config.site)
 
-        user1 = UserFactory.create(id=self.task.num_bins)
-        user2 = UserFactory.create(id=self.task.num_bins * 2)
+        user1 = UserFactory.create(id=self._next_user_id())
+        user2 = UserFactory.create(id=user1.id + self.task.num_bins)
         current_day, offset, target_day, upgrade_deadline = self._get_dates()
 
         self._schedule_factory(
@@ -323,7 +337,7 @@ class ScheduleSendEmailTestMixin(FilteredQueryCountMixin):
 
     @ddt.data(True, False)
     def test_course_end(self, has_course_ended):
-        user1 = UserFactory.create(id=self.task.num_bins)
+        user1 = UserFactory.create(id=self._next_user_id())
         current_day, offset, target_day, upgrade_deadline = self._get_dates()
 
         end_date_offset = -2 if has_course_ended else 2