test: fix timezone_not_near_midnight not to use pytz (ietf-tools#4678)

Author: jennifer-richards

ietf/utils/tests.py

@@ -491,13 +491,13 @@ class TimezoneTests(TestCase):
     def test_timezone_not_near_midnight(self, mock):
         # give it several choices that should be rejected and one that should be accepted
         with patch(
-                'ietf.utils.timezone.pytz.common_timezones',
-                [
+                'ietf.utils.timezone.available_timezones',
+                return_value=set([
                     'America/Chicago',  # time is 23:15, should be rejected
                     'America/Lima',  # time is 23:15, should be rejected
                     'America/New_York',  # time is 00:15, should be rejected
                     'Europe/Riga',  # time is 07:15, acceptable
-                ],
+                ]),
         ):
             # check a few times (will pass by chance < 0.1% of the time)
             self.assertEqual(timezone_not_near_midnight(), 'Europe/Riga')
@@ -508,12 +508,12 @@ def test_timezone_not_near_midnight(self, mock):
 
         # now give it no valid choice
         with patch(
-                'ietf.utils.timezone.pytz.common_timezones',
-                [
+                'ietf.utils.timezone.available_timezones',
+                return_value=set([
                     'America/Chicago',  # time is 23:15, should be rejected
                     'America/Lima',  # time is 23:15, should be rejected
                     'America/New_York',  # time is 00:15, should be rejected
-                ],
+                ]),
         ):
             with self.assertRaises(RuntimeError):
                 timezone_not_near_midnight()

ietf/utils/timezone.py

@@ -1,8 +1,9 @@
 import datetime
 import random
+import zoneinfo
 
 from typing import Union
-from zoneinfo import ZoneInfo
+from zoneinfo import available_timezones, ZoneInfo
 
 from django.conf import settings
 from django.utils import timezone
@@ -89,15 +90,17 @@ def timezone_not_near_midnight():
     Avoids midnight +/- 1 hour. Raises RuntimeError if it is unable to find
     a time zone satisfying this constraint.
     """
-    timezone_options = pytz.common_timezones
+    timezone_options = list(
+        available_timezones().difference(['Factory', 'localtime'])  # these two are not known to pytz
+    )
     tzname = random.choice(timezone_options)
-    right_now = timezone.now().astimezone(pytz.timezone(tzname))
+    right_now = timezone.now().astimezone(ZoneInfo(tzname))
     # Avoid the remote possibility of an infinite loop (might come up
     # if there is a problem with the time zone library)
     tries_left = 20
     while right_now.hour < 1 or right_now.hour >= 23:
         tzname = random.choice(timezone_options)
-        right_now = right_now.astimezone(pytz.timezone(tzname))
+        right_now = right_now.astimezone(ZoneInfo(tzname))
         tries_left -= 1
         if tries_left <= 0:
             raise RuntimeError('Unable to find a time zone not near midnight')