Fix conference day tests

src/core/tests/conference.py

-from datetime import datetime, timedelta
-
-import pytz
+from datetime import UTC, datetime, timedelta
+from unittest.mock import patch
 
 from django.test import TestCase
-from django.utils.timezone import now
+from django.utils import timezone
 
 from ..models.conference import Conference
 
@@ -14,22 +13,22 @@ class ConferenceTests(TestCase):
         self.conference.save()
 
     def test_get_conferenceday(self):
-        tz = pytz.timezone('Europe/Berlin')
-        self.conference.start = datetime(2042, 12, 27, 10, 00, tzinfo=tz)
-        self.conference.end = datetime(2042, 12, 30, 16, 00, tzinfo=tz)
-
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 24, 18, 00, tzinfo=tz)), -2)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 26, 12, 34, tzinfo=tz)), 0)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 27, 3, 45, tzinfo=tz)), 0)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 27, 12, 34, tzinfo=tz)), 1)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 30, 2, 34, tzinfo=tz)), 3)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 30, 12, 34, tzinfo=tz)), 4)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 31, 5, 30, tzinfo=tz)), 4)
-        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 31, 5, 30, tzinfo=tz)), 4)
+        self.conference.start = datetime(2042, 12, 27, 10, 00, tzinfo=UTC)
+        self.conference.end = datetime(2042, 12, 30, 16, 00, tzinfo=UTC)
+
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 24, 18, 00, tzinfo=UTC)), -2)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 26, 12, 34, tzinfo=UTC)), 0)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 27, 3, 45, tzinfo=UTC)), 0)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 27, 12, 34, tzinfo=UTC)), 1)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 30, 2, 34, tzinfo=UTC)), 3)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 30, 12, 34, tzinfo=UTC)), 4)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 31, 5, 30, tzinfo=UTC)), 4)
+        self.assertEqual(self.conference.get_conference_day(datetime(2042, 12, 31, 5, 30, tzinfo=UTC)), 4)
 
     def test_days_in(self):
-        self.conference.start = now() - timedelta(days=1)
-        self.conference.end = now() + timedelta(days=3)
+        with patch.object(timezone, 'now', return_value=datetime(2042, 12, 27, 12, 34, tzinfo=UTC)):
+            self.conference.start = timezone.now() - timedelta(days=1)
+            self.conference.end = timezone.now() + timedelta(days=3)
             self.assertTrue(self.conference.is_running)
             self.assertFalse(self.conference.has_ended)
             self.assertEqual(5, self.conference.days_count)
@@ -37,8 +36,9 @@ class ConferenceTests(TestCase):
             self.assertEqual(2, self.conference.current_day)
 
     def test_days_future(self):
-        self.conference.start = now() + timedelta(days=10)
-        self.conference.end = now() + timedelta(days=14)
+        with patch.object(timezone, 'now', return_value=datetime(2042, 12, 27, 12, 34, tzinfo=UTC)):
+            self.conference.start = timezone.now() + timedelta(days=10)
+            self.conference.end = timezone.now() + timedelta(days=14)
             self.assertFalse(self.conference.is_running)
             self.assertFalse(self.conference.has_ended)
             self.assertEqual(5, self.conference.days_count)
@@ -46,8 +46,9 @@ class ConferenceTests(TestCase):
             self.assertEqual(-9, self.conference.current_day)
 
     def test_days_past(self):
-        self.conference.start = now() - timedelta(days=5)
-        self.conference.end = now() - timedelta(days=2)
+        with patch.object(timezone, 'now', return_value=datetime(2042, 12, 27, 12, 34, tzinfo=UTC)):
+            self.conference.start = timezone.now() - timedelta(days=5)
+            self.conference.end = timezone.now() - timedelta(days=2)
             self.assertFalse(self.conference.is_running)
             self.assertTrue(self.conference.has_ended)
             self.assertEqual(4, self.conference.days_count)