Unit tests for the changes in abstract.c version 2.101. The debug

build's "undetected error" problems were originally detected with
extension types, but we can whitebox test the same situations with
new-style classes.

Lib/test/test_isinstance.py

+# Tests some corner cases with isinstance() and issubclass().  While these
+# tests use new style classes and properties, they actually do whitebox
+# testing of error conditions uncovered when using extension types.
+
+import unittest
+import test_support
+
+
+
+class TestIsInstanceWhitebox(unittest.TestCase):
+    # Test to make sure that an AttributeError when accessing the instance's
+    # class's bases is masked.  This was actually a bug in Python 2.2 and
+    # 2.2.1 where the exception wasn't caught but it also wasn't being cleared
+    # (leading to an "undetected error" in the debug build).  Set up is,
+    # isinstance(inst, cls) where:
+    #
+    # - inst isn't an InstanceType
+    # - cls isn't a ClassType, a TypeType, or a TupleType
+    # - cls has a __bases__ attribute
+    # - inst has a __class__ attribute
+    # - inst.__class__ as no __bases__ attribute
+    #
+    # Sounds complicated, I know, but this mimics a situation where an
+    # extension type raises an AttributeError when its __bases__ attribute is
+    # gotten.  In that case, isinstance() should return False.
+    def test_class_has_no_bases(self):
+        class I(object):
+            def getclass(self):
+                # This must return an object that has no __bases__ attribute
+                return None
+            __class__ = property(getclass)
+
+        class C(object):
+            def getbases(self):
+                return ()
+            __bases__ = property(getbases)
+
+        self.assertEqual(False, isinstance(I(), C()))
+
+    # Like above except that inst.__class__.__bases__ raises an exception
+    # other than AttributeError
+    def test_bases_raises_other_than_attribute_error(self):
+        class E(object):
+            def getbases(self):
+                raise RuntimeError
+            __bases__ = property(getbases)
+
+        class I(object):
+            def getclass(self):
+                return E()
+            __class__ = property(getclass)
+
+        class C(object):
+            def getbases(self):
+                return ()
+            __bases__ = property(getbases)
+
+        self.assertRaises(RuntimeError, isinstance, I(), C())
+
+    # Here's a situation where getattr(cls, '__bases__') raises an exception.
+    # If that exception is not AttributeError, it should not get masked
+    def test_dont_mask_non_attribute_error(self):
+        class I: pass
+
+        class C(object):
+            def getbases(self):
+                raise RuntimeError
+            __bases__ = property(getbases)
+
+        self.assertRaises(RuntimeError, isinstance, I(), C())
+
+    # Like above, except that getattr(cls, '__bases__') raises an
+    # AttributeError, which /should/ get masked as a TypeError
+    def test_mask_attribute_error(self):
+        class I: pass
+
+        class C(object):
+            def getbases(self):
+                raise AttributeError
+            __bases__ = property(getbases)
+
+        self.assertRaises(TypeError, isinstance, I(), C())
+
+
+
+# These tests are similar to above, but tickle certain code paths in
+# issubclass() instead of isinstance() -- really PyObject_IsSubclass()
+# vs. PyObject_IsInstance().
+class TestIsSubclassWhitebox(unittest.TestCase):
+    def test_dont_mask_non_attribute_error(self):
+        class C(object):
+            def getbases(self):
+                raise RuntimeError
+            __bases__ = property(getbases)
+
+        class S(C): pass
+
+        self.assertRaises(RuntimeError, issubclass, C(), S())
+
+    def test_mask_attribute_error(self):
+        class C(object):
+            def getbases(self):
+                raise AttributeError
+            __bases__ = property(getbases)
+
+        class S(C): pass
+        
+        self.assertRaises(TypeError, issubclass, C(), S())
+
+    # Like above, but test the second branch, where the __bases__ of the
+    # second arg (the cls arg) is tested.  This means the first arg must
+    # return a valid __bases__, and it's okay for it to be a normal --
+    # unrelated by inheritance -- class.
+    def test_dont_mask_non_attribute_error_in_cls_arg(self):
+        class B: pass
+
+        class C(object):
+            def getbases(self):
+                raise RuntimeError
+            __bases__ = property(getbases)
+
+        self.assertRaises(RuntimeError, issubclass, B, C())
+
+    def test_mask_attribute_error_in_cls_arg(self):
+        class B: pass
+
+        class C(object):
+            def getbases(self):
+                raise AttributeError
+            __bases__ = property(getbases)
+
+        self.assertRaises(TypeError, issubclass, B, C())
+
+
+
+def test_main():
+    suite = unittest.TestSuite()
+    suite.addTest(unittest.makeSuite(TestIsInstanceWhitebox))
+    suite.addTest(unittest.makeSuite(TestIsSubclassWhitebox))
+    test_support.run_suite(suite)
+
+
+if __name__ == '__main__':
+    test_main()