diff --git a/tests/file_storage/tests.py b/tests/file_storage/tests.py
index 04d4f0c8d6..19e8151dc8 100644
--- a/tests/file_storage/tests.py
+++ b/tests/file_storage/tests.py
@@ -94,9 +94,7 @@ class FileStorageDeconstructionTests(unittest.TestCase):
 requires_pytz = unittest.skipIf(pytz is None, "this test requires pytz")
 
 
-class FileStorageTests(TestCase):
-    # Changing TIME_ZONE may issue a query to set the database's timezone,
-    # hence TestCase.
+class FileStorageTests(SimpleTestCase):
     storage_class = FileSystemStorage
 
     def setUp(self):
diff --git a/tests/humanize_tests/tests.py b/tests/humanize_tests/tests.py
index e2fa66976a..22ae426954 100644
--- a/tests/humanize_tests/tests.py
+++ b/tests/humanize_tests/tests.py
@@ -6,7 +6,7 @@ from unittest import skipIf
 
 from django.contrib.humanize.templatetags import humanize
 from django.template import Context, Template, defaultfilters
-from django.test import TestCase, modify_settings, override_settings
+from django.test import SimpleTestCase, modify_settings, override_settings
 from django.utils import translation
 from django.utils.html import escape
 from django.utils.timezone import get_fixed_timezone, utc
@@ -36,7 +36,7 @@ class MockDateTime(datetime.datetime):
 
 
 @modify_settings(INSTALLED_APPS={'append': 'django.contrib.humanize'})
-class HumanizeTests(TestCase):
+class HumanizeTests(SimpleTestCase):
 
     def humanize_tester(self, test_list, result_list, method, normalize_result_func=escape):
         for test_content, result in zip(test_list, result_list):
diff --git a/tests/mail/tests.py b/tests/mail/tests.py
index 007ce2dc5c..bf8ea95e03 100644
--- a/tests/mail/tests.py
+++ b/tests/mail/tests.py
@@ -21,7 +21,7 @@ from django.core.mail import (
 )
 from django.core.mail.backends import console, dummy, filebased, locmem, smtp
 from django.core.mail.message import BadHeaderError, sanitize_address
-from django.test import SimpleTestCase, TestCase, override_settings
+from django.test import SimpleTestCase, override_settings
 from django.test.utils import requires_tz_support
 from django.utils._os import upath
 from django.utils.encoding import force_bytes, force_text
@@ -607,9 +607,8 @@ class MailTests(HeadersCheckMixin, SimpleTestCase):
 
 
 @requires_tz_support
-class MailTimeZoneTests(TestCase):
+class MailTimeZoneTests(SimpleTestCase):
 
-    # setting the timezone requires a database query on PostgreSQL.
     @override_settings(EMAIL_USE_LOCALTIME=False, USE_TZ=True, TIME_ZONE='Africa/Algiers')
     def test_date_header_utc(self):
         """
diff --git a/tests/timezones/tests.py b/tests/timezones/tests.py
index dce48f6eae..df9ac424c6 100644
--- a/tests/timezones/tests.py
+++ b/tests/timezones/tests.py
@@ -840,7 +840,7 @@ class SerializationTests(SimpleTestCase):
 
 
 @override_settings(DATETIME_FORMAT='c', TIME_ZONE='Africa/Nairobi', USE_L10N=False, USE_TZ=True)
-class TemplateTests(TestCase):
+class TemplateTests(SimpleTestCase):
 
     @requires_tz_support
     def test_localtime_templatetag_and_filters(self):