Set an environmental variable, but only for tests

[oakkitten]

I'm testing a Qt application and for some reason it needs to have HOME set. So I went and set it to a temporary folder:

[testenv]
setenv =
    HOME={envtmpdir}/home

This works fine, but I noticed that recreating the virtual environment takes an awfully long time. So I ran pip cache info in the env and apparently instead of /home/user/.cache/pip, it is using /home/user/project/.tox/py310-test/tmp/home/.cache/pip as the cache location. This means it downloads all dependencies for every environmnt. This is I guess because setenv is “used for all test command invocations as well as for installing the sdist package into a virtual environment”.

So, can I set an environmental variable only for test commands? Sorry if I'm missing some basic configuration bit.

[gaborbernat]

So, can I set an environmental variable only for test commands? Sorry if I'm missing some basic configuration bit.

No, you cannot and we don't plan to offer this functionality.

[oakkitten]

Sorry if I'm asking silly questions, but why not? And what can I do about this situation? I don't suppose needing HOME for tests is a rare enough occasion to ignore?

[oakkitten]

I just wonder if people simply do not notice this. In my case, 160MB of dependencies should be barely noticeable when the entire env takes up some 600MB and a long time to install even if the dependencies are cached—I just happened to be on a slow internet connection so I noticed that long is being way too long.

I might be able to get away with passenv, but when if you write your app configuration to HOME and want to test it, or need HOME for other reasons? If you grep the repos, there's quite a few examples of people setting their HOME with setenv. Perhaps this at least warrants a warning that if you set HOME, you are losing cache?

[gaborbernat]

I don't think needs the warning. If you set an environment variable you should understand the consequences of that. If you don't notice it then it's not a problem. If you do then you can work around by e.g. setting the PIP_CACHE_DIR as your true home folder. They are many env-vars that if you set things can get weird, HOME, PYTHONHOME, LDPATH, etc... I don't think it's the responsibility of the tool to hold your hand with each of them.

[oakkitten]

Call me stupid but I didn't realize that setenv also sets environmental variables for pip. Why? Well,

• for one, I think I got that bit from StackOverflow, which didn't mention that, and
• for another, with tox being very nice and straightforward on the whole, I just didn't expect that one directive sets the environment for both tests and env setup. These are two different tasks, right?
• but mostly, I didn't expect setenv to work like that because my tests didn't have HOME. My tests didn't have HOME, but I guess pip did have the cache, so it had HOME. So the machinery providing (at least HOME) for tests and for pip appeared to be different. I wouldn't imagine that setting HOME in setenv would have effect on both machineries.

Am I really being that unreasonable here?

If you don't notice it then it's not a problem.

It still leads to increased build times and data and disk usage, even if you don't notice it.

[gaborbernat]

It needs to affect pip, because if you want to use a custom index server the recommendation is to use the pip env var to set it. Many people expect setenv to impact the environment (all operations within it). Not just the commands. It probably would be comman_setenv named if that would be the case.

[oakkitten]

I understand that it's useful to have a directive that sets environmental variables for pip. And yes, many people would expect that setenv impacts all that is run in the env. Well, what can I say, I didn't ¯\_(ツ)_/¯. I'd love to use commands_setenv, that feels right. For now I guess I'll use the command env, as in below—with Qt, I don't want to risk any flakiness by using passenv. I only need HOME, so hey, this isn't too bad.

[testenv]
commands =
    env HOME={envtmpdir}/home python -m pytest