[Python-Dev] unittest isolation and warnings

[Brett Cannon]

Tests are not isolated from the warnings system, so things will leak out.
Your best option is to use the context manager in the warnings module to
temporarily make all warnings raise exceptions and test for the exception
(I'm at the airport, hence why I don't know the name of the context
manager; the warnings module docs actually have a sample on how best to
write tests the involve warnings).

On Fri, Nov 17, 2017, 01:34 Christian Tismer, <tismer at stackless.com> wrote:

> Hi guys,
>
> when writing tests, I suddenly discovered that unittest
> is not isolated to warnings.
>
> Example:
> One of my tests emits warnings when a certain condition is
> met. Instead of reporting the error immediately, it uses
> warnings, and at the end of the test, an error is produced
> if there were warnings.
>
>         if hasattr(__main__, "__warningregistry__"):
>             raise RuntimeError("There are errors, see above.")
>
> By chance, I discovered that an error was suddenly triggered without
> a warning. That must mean the warning existed already from
> another test as a left-over.
>
> My question:
> Is that known, and is that intended?
> To what extent are the test cases isolated from each other?
>
> I do admit that my usage of warnings is somewhat special.
> But it is very convenient to report many errors on remote servers.
>
> Cheers -- Chris
>
> --
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