On 3/28/2012 8:28 AM, Ulrich Eckhardt wrote:
Hi!
I'm currently writing some tests for the error handling of some code. In
this scenario, I must make sure that both the correct exception is
raised and that the contained error code is correct:
try:
foo()
self.fail('exception not raised')
catch MyException as e:
self.assertEqual(e.errorcode, SOME_FOO_ERROR)
catch Exception:
self.fail('unexpected exception raised')
This is tedious to write and read. The docs mention this alternative:
with self.assertRaises(MyException) as cm:
foo()
self.assertEqual(cm.the_exception.errorcode, SOME_FOO_ERROR)
Exceptions can have multiple attributes. This allows the tester to
exactly specify what attributes to test.
This is shorter, but I think there's an alternative syntax possible that
would be even better:
with self.assertRaises(MyException(SOME_FOO_ERROR)):
foo()
I presume that if this worked the way you want, all attributes would
have to match. The message part of builtin exceptions is allowed to
change, so hard-coding an exact expected message makes tests fragile.
This is a problem with doctest.
Here, assertRaises() is not called with an exception type but with an
exception instance. I'd implement it something like this:
def assertRaises(self, exception, ...):
# divide input parameter into type and instance
if isinstance(exception, Exception):
exception_type = type(exception)
else:
exception_type = exception
exception = None
# call testee and verify results
try:
...call function here...
except exception_type as e:
if not exception is None:
self.assertEqual(e, exception)
Did you use tabs? They do not get preserved indefinitely, so they are
bad for posting.
This of course requires the exception to be equality-comparable.
Equality comparison is by id. So this code will not do what you want.
You can, of course, write a custom AssertX subclass that at least works
for your custom exception class.
--
Terry Jan Reedy
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