bpo-35753: fix doctest on unwrappables funcs 1/2

Summary:

Ignore objects that inspect.unwrap throws due to
too many wrappers.  This is a very rare case, however
it can easily be surfaced when a module under doctest
imports unitest.mock.call into its namespace.

This commit adds a test that should fail prior to
the fix to the doctest module.

Test Plan:

Reviewers:

Subscribers:

Tasks:

Tags:

Author: splbio

Lib/test/test_doctest5.py

@@ -0,0 +1,33 @@
+"""A module to test whether doctest works properly with
+un-unwrappable functions.
+
+See: https://bugs.python.org/issue35753
+"""
+
+# This should trigger issue35753 when doctest called
+from unittest.mock import call
+
+import sys
+import unittest
+from test import support
+if sys.flags.optimize >= 2:
+    raise unittest.SkipTest("Cannot test docstrings with -O2")
+
+
+def test_main():
+    from test import test_doctest5
+    EXPECTED = 0
+    try:
+        f, t = support.run_doctest(test_doctest5)
+        if t != EXPECTED:
+            raise support.TestFailed("expected %d tests to run, not %d" %
+                                          (EXPECTED, t))
+    except ValueError as e:
+        raise support.TestFailed("Doctest unwrap failed") from e
+
+# Pollute the namespace with a bunch of imported functions and classes,
+# to make sure they don't get tested.
+# from doctest import *
+
+if __name__ == '__main__':
+    test_main()