test: avoid local times near midnight for test_past_swap_days_buttons() (#4642)

* test: avoid local times near midnight for test_past_swap_days_buttons()

* test: use timezone_options variable consistently

* test: add test of timezone_not_near_midnight() method

* fix: ensure that timezone_not_near_midnight() always exits

ietf/meeting/tests_js.py

@@ -34,6 +34,7 @@ from ietf.meeting.utils import add_event_info_to_session_qs
 from ietf.utils.test_utils import assert_ical_response_is_valid
 from ietf.utils.jstest import ( IetfSeleniumTestCase, ifSeleniumEnabled, selenium_enabled,
                                 presence_of_element_child_by_css_selector )
+from ietf.utils.timezone import timezone_not_near_midnight
 
 if selenium_enabled():
     from selenium.webdriver.common.action_chains import ActionChains
@@ -392,7 +393,12 @@ class EditMeetingScheduleTests(IetfSeleniumTestCase):
     def test_past_swap_days_buttons(self):
         """Swap days buttons should be hidden for past items"""
         wait = WebDriverWait(self.driver, 2)
-        meeting = MeetingFactory(type_id='ietf', date=datetime.datetime.today() - datetime.timedelta(days=3), days=7)
+        meeting = MeetingFactory(
+            type_id='ietf',
+            date=datetime.datetime.today() - datetime.timedelta(days=3),
+            days=7,
+            time_zone=timezone_not_near_midnight(),
+        )
         room = RoomFactory(meeting=meeting)
 
         # get current time in meeting time zone

ietf/utils/tests.py

@@ -2,12 +2,15 @@
 # -*- coding: utf-8 -*-
 
 
+import datetime
 import io
 import json
 import os.path
+import pytz
 import shutil
 import types
 
+from mock import patch
 from pyquery import PyQuery
 from typing import Dict, List       # pyflakes:ignore
 
@@ -39,6 +42,7 @@ from ietf.utils.mail import send_mail_preformatted, send_mail_text, send_mail_mi
 from ietf.utils.test_runner import get_template_paths, set_coverage_checking
 from ietf.utils.test_utils import TestCase, unicontent
 from ietf.utils.text import parse_unicode
+from ietf.utils.timezone import timezone_not_near_midnight
 from ietf.utils.xmldraft import XMLDraft
 
 class SendingMail(TestCase):
@@ -476,3 +480,40 @@ class TestAndroidSiteManifest(TestCase):
         manifest = json.loads(unicontent(r))
         self.assertTrue('name' in manifest)
         self.assertTrue('theme_color' in manifest)
+
+
+class TimezoneTests(TestCase):
+    """Tests of the timezone utilities"""
+    @patch(
+        'ietf.utils.timezone.timezone.now',
+        return_value=pytz.timezone('America/Chicago').localize(datetime.datetime(2022, 7, 1, 23, 15, 0)),  # 23:15:00
+    )
+    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',
+                [
+                    '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')
+            self.assertEqual(timezone_not_near_midnight(), 'Europe/Riga')
+            self.assertEqual(timezone_not_near_midnight(), 'Europe/Riga')
+            self.assertEqual(timezone_not_near_midnight(), 'Europe/Riga')
+            self.assertEqual(timezone_not_near_midnight(), 'Europe/Riga')
+
+        # now give it no valid choice
+        with patch(
+                'ietf.utils.timezone.pytz.common_timezones',
+                [
+                    '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 +1,11 @@
 import pytz
 import email.utils
 import datetime
+import random
 
 from django.conf import settings
+from django.utils import timezone
+
 
 def local_timezone_to_utc(d):
     """Takes a naive datetime in the local timezone and returns a
@@ -37,3 +40,23 @@ def email_time_to_local_timezone(date_string):
 def date2datetime(date, tz=pytz.utc):
     return datetime.datetime(*(date.timetuple()[:6]), tzinfo=tz)
     
+
+def timezone_not_near_midnight():
+    """Get the name of a random timezone where it's not close to midnight
+
+    Avoids midnight +/- 1 hour. Raises RuntimeError if it is unable to find
+    a time zone satisfying this constraint.
+    """
+    timezone_options = pytz.common_timezones
+    tzname = random.choice(timezone_options)
+    right_now = timezone.now().astimezone(pytz.timezone(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))
+        tries_left -= 1
+        if tries_left <= 0:
+            raise RuntimeError('Unable to find a time zone not near midnight')
+    return tzname