MNT Use pytest --import-mode=importlib

[lesteve]

This would get pytest assertion rewriting back with meson editable install after @fcharras's investigation of mesonbuild/meson-python#646.

--import-mode=importlib is what pytest recommends see their doc. The default prepend is an historical thing that they don't recommend and they probably don't want to change the default to not break backward-compatibility.

The recommendation was already the case for our minimum pytest version see 7.1.x doc.

This seems to be working fine locally, let's see what the CI has to say about it.

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[lesteve]

So the pytest assertion rewriting seems to work in all CI with this change I added a broken test on purpose see build log

_________________________________ test_broken __________________________________
[gw0] linux -- Python 3.13.3 /usr/share/miniconda/envs/testvenv/bin/python

    def test_broken():
>       assert 2 + 1 == 10
E       assert (2 + 1) == 10

Without --import-mode=importlib there is no detail on AssertionError:

_________________________________________________________________________________________________________________ test_broken __________________________________________________________________________________________________________________

    def test_broken():
>       assert 2 + 1 == 10
E       AssertionError

sklearn/tests/test_isotonic.py:712: AssertionError

Note that in my broken test the additional info is not very useful but in general can be a lot more useful e.g. something like this:

_________________________________________________________________________________________________________________ test_broken __________________________________________________________________________________________________________________

    def test_broken():
        X = np.arange(10).reshape(2, 5)
>       assert X.sum() == 10
E       assert np.int64(45) == 10
E        +  where np.int64(45) = <built-in method sum of numpy.ndarray object at 0x795048da1590>()
E        +    where <built-in method sum of numpy.ndarray object at 0x795048da1590> = array([[0, 1, 2, 3, 4],\n       [5, 6, 7, 8, 9]]).sum

sklearn/tests/test_isotonic.py:713: AssertionError

An historical case where pytest assertion rewriting was useful: #30315 (comment). An example where it was annoying not to have it: #29253 (comment).

[thomasjpfan]

LGTM

[jeremiedbb]

LGTM. I was wondering if the asserts were always like this but then I thought it was my memory playing with me. It was not apprently :) thx for the fix