Simplified timezones tests with settings_changed.

All relevant state is now properly reset whenever TIME_ZONE or USE_TZ
are changed in tests.

2 files changed, 22 insertions, 3 deletions

diff --git a/django/test/signals.py b/django/test/signals.py
index ed16831d42..81808dfa3c 100644
--- a/django/test/signals.py
+++ b/django/test/signals.py
@@ -1,27 +1,47 @@
+import os
+import time
+
 from django.conf import settings
 from django.db import connections
 from django.dispatch import receiver, Signal
 from django.template import context
+from django.utils import timezone
 
 template_rendered = Signal(providing_args=["template", "context"])
 
 setting_changed = Signal(providing_args=["setting", "value"])
 
+
 @receiver(setting_changed)
 def update_connections_time_zone(**kwargs):
+    if kwargs['setting'] == 'TIME_ZONE':
+        # Reset process time zone
+        if hasattr(time, 'tzset'):
+            if kwargs['value']:
+                os.environ['TZ'] = kwargs['value']
+            else:
+                os.environ.pop('TZ', None)
+            time.tzset()
+
+        # Reset local time zone cache
+        timezone._localtime = None
+
+    # Reset the database connections' time zone
     if kwargs['setting'] == 'USE_TZ' and settings.TIME_ZONE != 'UTC':
         USE_TZ, TIME_ZONE = kwargs['value'], settings.TIME_ZONE
     elif kwargs['setting'] == 'TIME_ZONE' and not settings.USE_TZ:
         USE_TZ, TIME_ZONE = settings.USE_TZ, kwargs['value']
-    else:   # no need to change the database connnections' time zones
+    else:
+        # no need to change the database connnections' time zones
         return
-
     tz = 'UTC' if USE_TZ else TIME_ZONE
     for conn in connections.all():
+        conn.settings_dict['TIME_ZONE'] = tz
         tz_sql = conn.ops.set_time_zone_sql()
         if tz_sql:
             conn.cursor().execute(tz_sql, [tz])
 
+
 @receiver(setting_changed)
 def clear_context_processors_cache(**kwargs):
     if kwargs['setting'] == 'TEMPLATE_CONTEXT_PROCESSORS':
diff --git a/django/utils/timezone.py b/django/utils/timezone.py
index 0bba97e736..d9d9636023 100644
--- a/django/utils/timezone.py
+++ b/django/utils/timezone.py
@@ -95,7 +95,6 @@ utc = pytz.utc if pytz else UTC()
 
 # In order to avoid accessing the settings at compile time,
 # wrap the expression in a function and cache the result.
-# If you change settings.TIME_ZONE in tests, reset _localtime to None.
 _localtime = None
 
 def get_default_timezone():