Added patch_formats utility for i18n formatting tests

tests/i18n/tests.py

@@ -1,6 +1,7 @@
 # -*- encoding: utf-8 -*-
 from __future__ import unicode_literals
 
+from contextlib import contextmanager
 import datetime
 import decimal
 from importlib import import_module
@@ -42,6 +43,18 @@ extended_locale_paths = settings.LOCALE_PATHS + (
     os.path.join(here, 'other', 'locale'),
 )
 
+@contextmanager
+def patch_formats(lang, **settings):
+    from django.utils.formats import _format_cache
+
+    # Populate _format_cache with temporary values
+    for key, value in settings.items():
+        _format_cache[(key, lang)] = value
+    try:
+        yield
+    finally:
+        reset_format_cache()
+
 
 class TranslationTests(TestCase):
 
@@ -482,17 +495,7 @@ class FormattingTests(TestCase):
         conditional test (e.g. 0 or empty string).
         Refs #16938.
         """
-        from django.conf.locale.fr import formats as fr_formats
-
-        # Back up original formats
-        backup_THOUSAND_SEPARATOR = fr_formats.THOUSAND_SEPARATOR
-        backup_FIRST_DAY_OF_WEEK = fr_formats.FIRST_DAY_OF_WEEK
-
-        # Set formats that would get interpreted as False in a conditional test
-        fr_formats.THOUSAND_SEPARATOR = ''
-        fr_formats.FIRST_DAY_OF_WEEK = 0
-
-        reset_format_cache()
+        with patch_formats('fr', THOUSAND_SEPARATOR='', FIRST_DAY_OF_WEEK=0):
             with translation.override('fr'):
                 with self.settings(USE_THOUSAND_SEPARATOR=True, THOUSAND_SEPARATOR='!'):
                     self.assertEqual('', get_format('THOUSAND_SEPARATOR'))
@@ -504,10 +507,6 @@ class FormattingTests(TestCase):
                     # Even a second time (after the format has been cached)...
                     self.assertEqual(0, get_format('FIRST_DAY_OF_WEEK'))
 
-        # Restore original formats
-        fr_formats.THOUSAND_SEPARATOR = backup_THOUSAND_SEPARATOR
-        fr_formats.FIRST_DAY_OF_WEEK = backup_FIRST_DAY_OF_WEEK
-
     def test_l10n_enabled(self):
         self.maxDiff = 3000
         # Catalan locale