Adjusted tests that were messing with database connections too heavily.

The previous implementation would result in tests hitting the wrong
database when running tests in parallel on multiple databases.

tests/timezones/tests.py

@@ -4,6 +4,7 @@ import datetime
 import re
 import sys
 import warnings
+from contextlib import contextmanager
 from unittest import SkipTest, skipIf
 from xml.dom.minidom import parseString
 
@@ -611,27 +612,41 @@ class ForcedTimeZoneDatabaseTests(TransactionTestCase):
             raise SkipTest("Database doesn't support feature(s): test_db_allows_multiple_connections")
 
         super(ForcedTimeZoneDatabaseTests, cls).setUpClass()
-        connections.databases['tz'] = connections.databases['default'].copy()
-        connections.databases['tz']['TIME_ZONE'] = 'Asia/Bangkok'
 
-    @classmethod
-    def tearDownClass(cls):
-        connections['tz'].close()
-        del connections['tz']
-        del connections.databases['tz']
-        super(ForcedTimeZoneDatabaseTests, cls).tearDownClass()
+    @contextmanager
+    def override_database_connection_timezone(self, timezone):
+        try:
+            orig_timezone = connection.settings_dict['TIME_ZONE']
+            connection.settings_dict['TIME_ZONE'] = timezone
+            # Clear cached properties, after first accessing them to ensure they exist.
+            connection.timezone
+            del connection.timezone
+            connection.timezone_name
+            del connection.timezone_name
+
+            yield
+
+        finally:
+            connection.settings_dict['TIME_ZONE'] = orig_timezone
+            # Clear cached properties, after first accessing them to ensure they exist.
+            connection.timezone
+            del connection.timezone
+            connection.timezone_name
+            del connection.timezone_name
 
     def test_read_datetime(self):
         fake_dt = datetime.datetime(2011, 9, 1, 17, 20, 30, tzinfo=UTC)
         Event.objects.create(dt=fake_dt)
 
-        event = Event.objects.using('tz').get()
-        dt = datetime.datetime(2011, 9, 1, 10, 20, 30, tzinfo=UTC)
+        with self.override_database_connection_timezone('Asia/Bangkok'):
+            event = Event.objects.get()
+            dt = datetime.datetime(2011, 9, 1, 10, 20, 30, tzinfo=UTC)
         self.assertEqual(event.dt, dt)
 
     def test_write_datetime(self):
         dt = datetime.datetime(2011, 9, 1, 10, 20, 30, tzinfo=UTC)
-        Event.objects.using('tz').create(dt=dt)
+        with self.override_database_connection_timezone('Asia/Bangkok'):
+            Event.objects.create(dt=dt)
 
         event = Event.objects.get()
         fake_dt = datetime.datetime(2011, 9, 1, 17, 20, 30, tzinfo=UTC)