[pytest-dev] Pytest fails with the wrong error when unicode_literals is present

[Bruno Oliveira]

Hi everyone,

Besides the problem that reinterpret is executing code in a context without
unicode_literals enabled, this also showcases that when moving a fixture
with has asserts on it from a test file to a conftest file, asserts will
not be rewritten anymore and reinterpretation will be used instead, which
might cause unexpected issues, as illustrated by Gustavo.

The first issue looks like a bug to me, not sure what to do about this
second point. Any thoughts?

Cheers,

On Mon, Nov 24, 2014 at 1:51 PM, Edison Gustavo Muenz <
edisongustavo at gmail.com> wrote:

> TL;DR;
>
> The eval() method of the Frame object is not “inheriting” the __future__
> imports from the frame.
> Long explanation
>
> Suppose I have a fixture in which I write my assert statements. If this
> fixture has strings on the assert statement then when the assert fails I
> get the wrong kind of errors.
>
> The problem is that the pytest assertion rewrite mechanism is calling
> eval() on the code that contains the frame
>
> To better illustrate what happens, see this gist
> <https://gist.github.com/edisongustavo/5533a1c36de6cab6f39a>
>
> The tests
> <https://gist.github.com/edisongustavo/5533a1c36de6cab6f39a#file-test_unicode_error_with_plugin_fixture-py>
> have the following output:
>
>    - test_plugin_fixture - *fail*
>    - test_conftest_fixture - *fail*
>    - test_inline_fixture - pass
>    - test_no_fixture - pass
>
> The output of *test_plugin_fixture* (omitted some output for brevity):
>
> $ pytest -k test_plugin_fixture
>
>         msg = e.value.msg
> >       assert msg.startswith('assert <classes.ValueAndString object'), msg
> E       AssertionError: ValueError: ValueAndString(2, 'lkajflaskjfalskf')  << Error!
>
> While debugging I found out that the ValueAndString constructor was being
> called 3 times, instead of 2. The 3rd call happened in code.py:100, which
> is part of the py lib <https://bitbucket.org/hpk42/py> library. The
> “wrong” behaviour can be seen on the run_pyframe_eval.py
> <https://gist.github.com/edisongustavo/5533a1c36de6cab6f39a#file-run_pyframe_eval-py>
> .
>
> I’ve tested this code on Pytest 2.6.4 with Python 2.7.8 in Windows 7 -
> 64bits.
> ​
>
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