Refs #35361 -- Added test for Email line length checks when dealing with surrogate pairs.

Refs #33173, #34118 and #34900.

tests/mail/tests.py

@@ -92,6 +92,37 @@ class MailTests(HeadersCheckMixin, SimpleTestCase):
         self.assertEqual(message["From"], "from@example.com")
         self.assertEqual(message["To"], "to@example.com")
 
+    @mock.patch("django.core.mail.message.MIMEText.set_payload")
+    def test_nonascii_as_string_with_ascii_charset(self, mock_set_payload):
+        """Line length check should encode the payload supporting `surrogateescape`.
+
+        Following https://github.com/python/cpython/issues/76511, newer
+        versions of Python (3.11.9, 3.12.3 and 3.13) ensure that a message's
+        payload is encoded with the provided charset and `surrogateescape` is
+        used as the error handling strategy.
+
+        This test is heavily based on the test from the fix for the bug above.
+        Line length checks in SafeMIMEText's set_payload should also use the
+        same error handling strategy to avoid errors such as:
+
+        UnicodeEncodeError: 'utf-8' codec can't encode <...>: surrogates not allowed
+
+        """
+
+        def simplified_set_payload(instance, payload, charset):
+            instance._payload = payload
+
+        mock_set_payload.side_effect = simplified_set_payload
+
+        text = (
+            "Text heavily based in Python's text for non-ascii messages: Föö bär"
+        ).encode("iso-8859-1")
+        body = text.decode("ascii", errors="surrogateescape")
+        email = EmailMessage("Subject", body, "from@example.com", ["to@example.com"])
+        message = email.message()
+        mock_set_payload.assert_called_once()
+        self.assertEqual(message.get_payload(decode=True), text)
+
     def test_multiple_recipients(self):
         email = EmailMessage(
             "Subject",