pytest required to use yt.testing

[chrishavlin]

This is likely a bit of an edge case, but because we import pytest at the top of yt.testing, one needs pytest installed to import yt.testing.

I commonly use the fake_ datasets in various ways, often in fresh environments and I know of at least one place in the docs where we explicitly import yt.testing (https://yt-project.org/doc/examining/loading_via_functions.html), both of which result in import errors if you only do a pip install yt or even a pip install yt[full].

Any objection to me fixing that?

I the minimal fix is to just move that import pytest to within the only function that uses it (requires_module_pytest). alternatively, I think yt.testing has grown to the point where it might make sense to split it up a bit -- maybe move all of the fake_ dataset constructors to their own module in order to separate dataset construction from test execution utilities?

[matthewturk]

I also ran into this! I think moving the fake stuff somewhere else would be fine, or even hiding it inside something like load_sample() somehow, I dunno.

[neutrinoceros]

For context #3771
No objection to nesting the imports. Splitting the module may not be worth the backward compatibility layer needed to not break downstream users.

[chrishavlin]

Oh! I remember that discussion now. Thanks for the reminder!

I'll think a bit about splitting the module, but if it gets annoying I'll settle for moving the import... more soon...

[chrishavlin]

Ok, splitting out the fake_ datasets did indeed prove rather annoying... I may think more about that in the future, but for now I just submitted a PR that simply nests the pytest import.