Simon Connah via Tutor wrote:
> Hi,
> I'm just wondering what the accepted way to handle unit testing exceptions
> is? I know you are meant to use assertRaises, but my code seems a little
> off.
> try:
> some_func()
> except SomeException:
> self.assertRaises(SomeException)
The logic is wrong here as you surmise below. If you catch the exception
explicitly you have to write
try:
some_func()
except SomeException:
pass # OK
else:
self.fail("no exception raised")
Alternatively you can write
self.assertRaises(SomeException, some_func)
which is already better, but becomes a bit hard to read once some_func takes
arguments:
self.assertRaises(SomeException, some_func, "one", two=42)
Therefore I recommend using assertRaises() as a context manager:
with self.assertRaises(SomeException):
some_func("one", two=42)
This has the advantage that some_func() appears with its args as it would in
normal code, and that you can also test expressions:
with self.assertRaises(ZeroDivisionError):
MyNumber(1)/0
> Is there a better way to do this at all?
> The problem with the above code is that if no exception is raised the code
> completely skips the except block and that would mean that the unit test
> would pass so, I considered adding: self.fail('No exception raised') at
> the end outside of the except block but not sure if that is what I need to
> do. Any help is appreciated.
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