python · vstinner · Aug 11, 2020 · Aug 3, 2020
diff --git a/Lib/test/libregrtest/utils.py b/Lib/test/libregrtest/utils.py
@@ -72,7 +72,12 @@ def regrtest_unraisable_hook(unraisable):
    global orig_unraisablehook
    support.environment_altered = True
    print_warning("Unraisable exception")
-    orig_unraisablehook(unraisable)
+    old_stderr = sys.stderr
+    try:
+        sys.stderr = sys.__stderr__
+        orig_unraisablehook(unraisable)
+    finally:
+        sys.stderr = old_stderr


 def setup_unraisable_hook():

diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
@@ -1234,10 +1234,12 @@ def test_sleep(self):
                         re.compile('%s timed out' % testname, re.MULTILINE))

    def test_unraisable_exc(self):
-        # --fail-env-changed must catch unraisable exception
+        # --fail-env-changed must catch unraisable exception.
+        # The exceptioin must be displayed even if sys.stderr is redirected.
        code = textwrap.dedent(r"""
            import unittest
            import weakref
+            from test.support import captured_stderr

            class MyObject:
                pass
@@ -1249,9 +1251,11 @@ class Tests(unittest.TestCase):
                def test_unraisable_exc(self):
                    obj = MyObject()
                    ref = weakref.ref(obj, weakref_callback)
-                    # call weakref_callback() which logs
-                    # an unraisable exception
-                    obj = None
+                    with captured_stderr() as stderr:
+                        # call weakref_callback() which logs
+                        # an unraisable exception
+                        obj = None
+                    self.assertEqual(stderr.getvalue(), '')
        """)
        testname = self.create_test(code=code)

@@ -1260,6 +1264,7 @@ def test_unraisable_exc(self):
                                  env_changed=[testname],
                                  fail_env_changed=True)
        self.assertIn("Warning -- Unraisable exception", output)
+        self.assertIn("Exception: weakref callback bug", output)

    def test_cleanup(self):
        dirname = os.path.join(self.tmptestdir, "test_python_123")