[TIP] Some proposed additions to unittest.mock

Julian Berman julian at grayvines.com
Mon Apr 15 10:35:02 PDT 2013

On Apr 15, 2013 1:11 PM, "Chris Conway" <clconway at google.com> wrote:
> I've recently started using the mock library in my code (transitioning
from Mox) and I really like it a lot. There's a few little utilities I've
written for myself and I wonder if you'd accept them as patches.
> First, I find that I strongly prefer to use autospecced instances for
most of my mocks. To make that simpler, I wrote a create_strictspec()
function as a wrapper around create_autospec() with instance=True.
> I also find that I frequently want a mock function that should never be
called (e.g., in a test where I'm patching open() and testing a code path
where no file is opened). This can be asserted ex post by checking
call_count, but then you don't get any information about where the call
occurred. Alternatively, you can use a NoncallableMock, but then you get a
fairly opaque error: "TypeError: 'NonCallableMock' object is not callable".
I find it preferable to use a utility method expect_never_called() to set
an AssertionError side effect on the mock.

I find this error message to be pretty transparent honestly.

Hypothetically though, Mock's assertions are all state based and done after
exercising, so starting to add preconfigured expectations would seem out of
place to me. I personally wouldn't mind terribly much if you wanted to
change the error message to say something more mock-specific, but nothing
comes to me at the moment that would beat the current message.

I don't have a meaningful opinion on the first thing since unfortunately I
don't use tightly spec'ed mocks as much as I should, mostly out of laziness
:/. But it'd have to be fairly common to deserve a separate function for a
single parameter.

(Would love to hear more things you come up with coming from Mox certainly,
there was someone else in the IRC channel who was discussing it [maybe that
was you?])


> Do you think these would be helpful additions to the library?
> Best regards,
> Chris
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