Method assertRaises

Lib/unittest/case.py:783–814

Fail unless an exception of class expected_exception is raised by the callable when invoked with specified positional and keyword arguments. If a different type of exception is raised, it will not be caught, and the test case will be deemed to have suffere

(self, expected_exception, *args, **kwargs)

            return  '%s : %s' % (safe_repr(standardMsg), safe_repr(msg))

    def assertRaises(self, expected_exception, *args, **kwargs):
        """Fail unless an exception of class expected_exception is raised
           by the callable when invoked with specified positional and
           keyword arguments. If a different type of exception is
           raised, it will not be caught, and the test case will be
           deemed to have suffered an error, exactly as for an
           unexpected exception.

           If called with the callable and arguments omitted, will return a
           context object used like this::

                with self.assertRaises(SomeException):
                    do_something()

           An optional keyword argument 'msg' can be provided when assertRaises
           is used as a context object.

           The context manager keeps a reference to the exception as
           the 'exception' attribute. This allows you to inspect the
           exception after the assertion::

               with self.assertRaises(SomeException) as cm:
                   do_something()
               the_exception = cm.exception
               self.assertEqual(the_exception.error_code, 3)
        """
        context = _AssertRaisesContext(expected_exception, self)
        try:
            return context.handle('assertRaises', args, kwargs)
        finally:
            # bpo-23890: manually break a reference cycle
            context = None

    def assertWarns(self, expected_warning, *args, **kwargs):
        """Fail unless a warning of class warnClass is triggered