When patching an Exception with a side_effect to another exception, it seems like the exceiption arguments are not passed to the mock.

Currently, the exception is not instantiated. Maybe we can check if it's callable and pass args, kwargs to the exception constructor to be raised.

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index a48132c5b1..f5bcb911f5 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -1145,7 +1145,10 @@ class CallableMixin(Base):
         effect = self.side_effect
         if effect is not None:
             if _is_exception(effect):
-                raise effect
+                if _callable(effect):
+                    raise effect(*args, **kwargs)
+                else:
+                    raise effect
             elif not _callable(effect):
                 result = next(effect)
                 if _is_exception(result):

Not sure this is correct, if an effect is an exception and requires args, then it should be passed as an instance, not a class:

Mock(side_effect=MyException(‘foo’))

> On 10 Nov 2019, at 04:49, Karthikeyan Singaravelan <report@bugs.python.org> wrote:
> 
> 
> Karthikeyan Singaravelan <tir.karthi@gmail.com> added the comment:
> 
> Currently, the exception is not instantiated. Maybe we can check if it's callable and pass args, kwargs to the exception constructor to be raised.
> 
> diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
> index a48132c5b1..f5bcb911f5 100644
> --- a/Lib/unittest/mock.py
> +++ b/Lib/unittest/mock.py
> @@ -1145,7 +1145,10 @@ class CallableMixin(Base):
>         effect = self.side_effect
>         if effect is not None:
>             if _is_exception(effect):
> -                raise effect
> +                if _callable(effect):
> +                    raise effect(*args, **kwargs)
> +                else:
> +                    raise effect
>             elif not _callable(effect):
>                 result = next(effect)
>                 if _is_exception(result):
> 
> ----------
> nosy: +cjw296, lisroach, mariocj89, michael.foord
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue38757>
> _______________________________________

The reason why it seems that "no arguments are beeing passed" is because the exception is not being raised by you, but by mock itself when the exception is trying to be created. When an exception type is passed as side_effect, the mock modules raises such exception on the callable (the creation of the initial exception) To confirm this, just try removing the "raise" and leave the creation of the exception only.

I'd suggest that you use `wraps` rather than `side_effect`. That will make your example work.

Alternatively, if you need to use `side_effect`, you can use a wrapper so mock won't raise an exception when it sees that one:

```

def wrapper(*args, **kwargs):
    return MockError(*args, **kwargs)

patcher = patch('__main__.ProductionError', side_effect=wrapper)

```


I think this can be closed as a non-issue.

Agreed.