> +    (arguments
> +     '(#:phases
> +       (modify-phases %standard-phases
> +         (replace 'check
> +           (lambda _ (invoke "pytest"))))))

I'm a bit late, as this has already been merged,
but this should have been something like:

> +         (replace 'check
> +           (lambda* (#:key tests? #:allow-other-keys)
> +             (when tests?
> +               (invoke "pytest")))))))

That way, tests can be disabled with "--without-tests".
Try "./pre-inst-env guix build pytest --without-tests=pytests".
Respecting #:tests? can also be important for cross-compilation.

Could you send a follow-up patch, or could someone directly
commit such a change?

Greetings,
Maxime.