[Python-checkins] python/dist/src/Lib/test test_isinstance.py,NONE,1.1

[bwarsaw@sourceforge.net]

Update of /cvsroot/python/python/dist/src/Lib/test
In directory usw-pr-cvs1:/tmp/cvs-serv20676

Added Files:
	test_isinstance.py 
Log Message:
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.


--- NEW FILE: 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()