[Python-Dev] unittest isolation and warnings (original) (raw)

Brett Cannon brett at python.org
Fri Nov 17 10:44:06 EST 2017

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 -- Christian Tismer :^) tismer at stackless.com Software Consulting : http://www.stackless.com/ Karl-Liebknecht-Str. 121 : https://github.com/PySide 14482 Potsdam : GPG key -> 0xFB7BEE0E phone +49 173 24 18 776 fax +49 (30) 700143-0023

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