gh-115133: Fix tests for XMLPullParser with Expat 2.6.0 (GH-115164)

Feeding the parser by too small chunks defers parsing to prevent
CVE-2023-52425. Future versions of Expat may be more reactive.

Lib/test/test_xml_etree.py

@@ -13,6 +13,7 @@ import itertools
 import operator
 import os
 import pickle
+import pyexpat
 import sys
 import textwrap
 import types
@@ -120,6 +121,10 @@ ATTLIST_XML = """\
 </foo>
 """
 
+fails_with_expat_2_6_0 = (unittest.expectedFailure
+                        if pyexpat.version_info >= (2, 6, 0) else
+                        lambda test: test)
+
 def checkwarnings(*filters, quiet=False):
     def decorator(test):
         def newtest(*args, **kwargs):
@@ -1480,9 +1485,7 @@ class XMLPullParserTest(unittest.TestCase):
         self.assertEqual([(action, elem.tag) for action, elem in events],
                          expected)
 
-    def test_simple_xml(self):
-        for chunk_size in (None, 1, 5):
-            with self.subTest(chunk_size=chunk_size):
+    def test_simple_xml(self, chunk_size=None):
         parser = ET.XMLPullParser()
         self.assert_event_tags(parser, [])
         self._feed(parser, "<!-- comment -->\n", chunk_size)
@@ -1503,6 +1506,17 @@ class XMLPullParserTest(unittest.TestCase):
         self.assert_event_tags(parser, [('end', 'root')])
         self.assertIsNone(parser.close())
 
+    @fails_with_expat_2_6_0
+    def test_simple_xml_chunk_1(self):
+        self.test_simple_xml(chunk_size=1)
+
+    @fails_with_expat_2_6_0
+    def test_simple_xml_chunk_5(self):
+        self.test_simple_xml(chunk_size=5)
+
+    def test_simple_xml_chunk_22(self):
+        self.test_simple_xml(chunk_size=22)
+
     def test_feed_while_iterating(self):
         parser = ET.XMLPullParser()
         it = parser.read_events()

Misc/NEWS.d/next/Library/2024-02-08-14-21-28.gh-issue-115133.ycl4ko.rst

@@ -0,0 +1,2 @@
+Fix tests for :class:`~xml.etree.ElementTree.XMLPullParser` with Expat
+2.6.0.