Fixed #25191 -- Added string diff to SimpleTestCase.assertXMLEqual() message.

django/test/testcases.py

@@ -784,6 +784,13 @@ class SimpleTestCase(unittest.TestCase):
         else:
             if not result:
                 standardMsg = '%s != %s' % (safe_repr(xml1, True), safe_repr(xml2, True))
+                diff = ('\n' + '\n'.join(
+                    difflib.ndiff(
+                        six.text_type(xml1).splitlines(),
+                        six.text_type(xml2).splitlines(),
+                    )
+                ))
+                standardMsg = self._truncateMessage(standardMsg, diff)
                 self.fail(self._formatMessage(msg, standardMsg))
 
     def assertXMLNotEqual(self, xml1, xml2, msg=None):

tests/test_utils/tests.py

@@ -710,6 +710,19 @@ class XMLEqualTests(SimpleTestCase):
         with self.assertRaises(AssertionError):
             self.assertXMLEqual(xml1, xml2)
 
+    def test_simple_equal_raises_message(self):
+        xml1 = "<elem attr1='a' />"
+        xml2 = "<elem attr2='b' attr1='a' />"
+
+        msg = '''{xml1} != {xml2}
+- <elem attr1='a' />
++ <elem attr2='b' attr1='a' />
+?      ++++++++++
+'''.format(xml1=repr(xml1), xml2=repr(xml2))
+
+        with self.assertRaisesMessage(AssertionError, msg):
+            self.assertXMLEqual(xml1, xml2)
+
     def test_simple_not_equal(self):
         xml1 = "<elem attr1='a' attr2='c' />"
         xml2 = "<elem attr1='a' attr2='b' />"