Fixed #23883 -- Stopped flatatt modifying its argument

1 files changed, 17 insertions, 0 deletions

diff --git a/tests/forms_tests/tests/test_util.py b/tests/forms_tests/tests/test_util.py
index 68ecd50e99..c37affeb31 100644
--- a/tests/forms_tests/tests/test_util.py
+++ b/tests/forms_tests/tests/test_util.py
@@ -27,6 +27,23 @@ class FormsUtilTestCase(TestCase):
         self.assertEqual(flatatt({'class': "news", 'title': "Read this", 'required': False}), ' class="news" title="Read this"')
         self.assertEqual(flatatt({}), '')
 
+    def test_flatatt_no_side_effects(self):
+        """
+        Fixes #23883 -- Check that flatatt does not modify the dict passed in
+        """
+        attrs = {'foo': 'bar', 'true': True, 'false': False}
+        attrs_copy = copy.copy(attrs)
+        self.assertEqual(attrs, attrs_copy)
+
+        first_run = flatatt(attrs)
+        self.assertEqual(attrs, attrs_copy)
+        self.assertEqual(first_run, ' foo="bar" true')
+
+        second_run = flatatt(attrs)
+        self.assertEqual(attrs, attrs_copy)
+
+        self.assertEqual(first_run, second_run)
+
     def test_validation_error(self):
         ###################
         # ValidationError #