No assertion rewriting in files imported from conftest

[The-Compiler]

I guess I can't be the only one importing some utility code from conftest.py, or can I? 😉

With this conftest.py:

import pytest
from testutils import SomeClass

@pytest.fixture
def some_obj():
    return SomeClass()

And a testutils.py:

class SomeClass():

    def __init__(self):
        x = 23
        y = 42
        assert x + y == 1337

And a test_foo.py:

def test_foo(some_obj):
    pass

With pytest 2.9, I guess assertion reinterpretion kicks in and I get:

>       assert x + y == 1337
E       AssertionError

With 3.0, that's removed and I get plain asserts:

>       assert x + y == 1337
E       AssertionError

Since I have some custom assertion helpers and stuff in separated files, that's quite a bummer.

I'm not sure what the best way to fix this would be - ideas I had so far:

• Rewrite everything under the testpath if an explicit one is given
• Rewrite everything in directories where there are conftest.py files
• Rewrite everything imported from conftest.py files (probably cleanest, but maybe hard to implement?)

[nicoddemus]

You will have to call register_assert_rewrite before trying to import testutils:

import pytest
pytest.register_assert_rewrite('testutils')
from testutils import SomeClass

@pytest.fixture
def some_obj():
    return SomeClass()

This now works as expected:

    def __init__(self):
        x = 23
        y = 42
>       assert x + y == 1337
E       assert (23 + 42) == 1337

[The-Compiler]

Oh - thanks, that worked beautifully (even with a package)!

Do you think we should do something automatically (like I outlined above) or should I close this? I don't really have a strong opinion on it.

[nicoddemus]

Rewrite everything under the testpath if an explicit one is given

This would mean that projects which decide to place tests next to the code would get their own non-test code rewritten, which is something @flub and @RonnyPfannschmidt are against (and with good reason).

Rewrite everything in directories where there are conftest.py files

Same problem as above.

Rewrite everything imported from conftest.py files (probably cleanest, but maybe hard to implement?)

That might not be safe as well because conftest.py files can easily import application code to implement fixtures etc.

I would really love some way to automate this in some way, but I don't really have an idea for that at the moment. 😁

[flub]

Ideally you'd do that register_assert_rewrite() in the __init__.py.

More importantly however is that you did not find the documentation for this when you upgraded to 3.0. How can we improve that?

[nicoddemus]

Ideally you'd do that register_assert_rewrite() in the init.py.

Agreed, it's just that @The-Compiler's test suite doesn't have any __init__.py files.

More importantly however is that you did not find the documentation for this when you upgraded to 3.0. How can we improve that?

Good point. We have some docs here already, but maybe we should've mentioned that more prominently on the CHANGELOG, I don't know... suggestions are welcome.

[The-Compiler]

Agreed, it's just that @The-Compiler's test suite doesn't have any __init__.py files.

Do we have some agreed-upon recommendation whether to do that or not yet? Seems like the answer changes depending on whom I ask 😆

More importantly however is that you did not find the documentation for this when you upgraded to 3.0. How can we improve that?

As Bruno pointed out, what I usually do when doing an upgrade (and certainly with a major one) is reading the changelog. register_assert_rewrite seems to be not mentioned at all - something like this would've helped me:

• Reinterpretation mode has now been removed. Only plain and rewrite mode are available, consequently the --assert=reinterp option is no longer available. This also means files imported from conftest.py will not benefit from improved assertions by default, you should use pytest.register_assert_rewrite to explicitly turn assertion rewriting on for those files. Thanks @flub for the PR.

[nicoddemus]

FWIW I think it is still valid to add that to the CHANGELOG, it might be helpful for someone else down the road. 😁