Module already imported warning

[jacebrowning]

When I run my tests using pytest==3.0.6 and pytest-cov==2.4.0, I see the following warning:

======================= pytest-warning summary ======================
WP1 None Module already imported so can not be re-written: pytest_cov
============ 1 passed, 1 pytest-warnings in 0.09 seconds ============

which unfortunately causes pytest to return a non-zero exit code and make the test suite as failing.

---

I don't see this warning with pytest==2.9.2.

If it helps, I found a similar issue reported in another library: pytest-dev/pytest-testinfra#125

[ionelmc]

Do you get other errors? AFAIK a mere warning can't change the exit code so the cause must be something else (some related exception somewhere?!)

[jacebrowning]

I think I overstated the problem.

I'm running my tests using pytest-watch and its not continuing on to my onpass command after displaying the warning (whereas it does continue with pytest==2.9.2 when no warning is displayed).

[ionelmc]

Isn't that an issue in pytest-watch then?

About the warning's source - are you importing pytest_cov in your code or how can I reproduce it?

[jacebrowning]

Sorry, I'm not really sure. 😄

I am not importing from pytest_cov or any other plugin, but pytest-cov is the only plugin reporting this warning.

[ionelmc]

Are you using xdist?

Hard to guess what the cause is. Can you make a reproducing example?

[nicoddemus]

Just to clarify, that warning is happening because by the time pytest is importing pytest_cov as a plugin and attempting to rewrite asserts on it, it already has been imported by someone else. Perhaps that might give a clue about who's importing it.

At a glance, I think the order is:

1. plugins specified by the -p option;
2. plugins installed in the environment (setuptools entry points);
3. PYTEST_PLUGINS environment variable.

[alejandrodnm]

I've just started using xdist and running pytest -f and got the same error:

$ pip freeze | grep pytest
pytest==3.0.6
pytest-cov==2.4.0
pytest-django==3.1.2
pytest-mock==1.5.0
pytest-poo-fail==1.1
pytest-timeit==0.3.0
pytest-xdist==1.15.0

Also it created some new coverage files

$ git status
...
Untracked files:
  (use "git add <file>..." to include in what will be committed)

        .coverage.my_hostname.1219.136209
        .coverage.my_hostname.1219.618935

I'm also getting wrong results when running with the -f flag

 $ pytest -f
============================================================================================================================= test session starts =============================================================================================================================$
platform linux -- Python 3.5.3, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
Django settings: config.settings.tests (from environment variable)
rootdir: /home/user/dev/sp/mad-project, inifile: pytest.ini
plugins: xdist-1.15.0, timeit-0.3.0, poo-fail-1.1, mock-1.5.0, django-3.1.2, cov-2.4.0, celery-4.0.2
collected 78 items
collected 78 items

mad/base/tests/test_admins.py .
mad/base/tests/test_consumers.py ..
mad/builds/tests/test_models.py ............
mad/builds/tests/test_serializers.py ........
mad/builds/tests/test_views.py ..............
mad/projects/tests/test_fields.py ...........
mad/projects/tests/test_models.py ...
mad/projects/tests/test_permissions.py ....
mad/projects/tests/test_serializers.py .........
mad/projects/tests/test_views.py ............
mad/users/tests/test_views.py ..

----------- coverage: platform linux, python 3.5.3-final-0 -----------
Name                          Stmts   Miss  Cover   Missing
-----------------------------------------------------------
mad/base/views.py                 4      0   100%   
mad/builds/admin.py               5      5     0%   1-7
mad/builds/filters.py             7      0   100%   
mad/builds/models.py             78     38    51%   1-26, 30-42, 45, 62, 70, 89, 131, 144
mad/builds/permissions.py         4      0   100%   
mad/builds/serializers.py        46      0   100%   
mad/builds/tasks.py              10     10     0%   1-16
mad/builds/views.py              64      0   100%   
mad/consumers.py                  4      0   100%   
mad/downloads/models.py           9      9     0%   1-13
mad/projects/admin.py             8      8     0%   1-12
mad/projects/fields.py           41      0   100%   
mad/projects/models.py           46     25    46%   1-20, 23, 46, 94-119
mad/projects/permissions.py      17      0   100%   
mad/projects/serializers.py      57      0   100%   
mad/projects/views.py            12      0   100%   
mad/urls.py                       9      0   100%   
mad/users/views.py               10      0   100%   
-----------------------------------------------------------
TOTAL                           431     95    78%   


============================================================================================================================ pytest-warning summary ===========================================================================================================================$
WP1 None Module already imported so can not be re-written: pytest_cov
================================================================================================================ 78 passed, 1 pytest-warnings in 14.63 seconds ================================================================================================================$
############################################################################################################################# waiting for changes #############################################################################################################################$
### Watching:   /home/user/dev/sp/mad-project

$ pytest
============================================================================================================================= test session starts ==============================================================================================================================
platform linux -- Python 3.5.3, pytest-3.0.6, py-1.4.32, pluggy-0.4.0
Django settings: config.settings.tests (from ini file)
rootdir: /home/user/dev/sp/mad-project, inifile: pytest.ini
plugins: xdist-1.15.0, timeit-0.3.0, poo-fail-1.1, mock-1.5.0, django-3.1.2, cov-2.4.0, celery-4.0.2
collected 78 items 

mad/base/tests/test_admins.py .
mad/base/tests/test_consumers.py ..
mad/builds/tests/test_models.py ............
mad/builds/tests/test_serializers.py ........
mad/builds/tests/test_views.py ..............
mad/projects/tests/test_fields.py ...........
mad/projects/tests/test_models.py ...
mad/projects/tests/test_permissions.py ....
mad/projects/tests/test_serializers.py .........
mad/projects/tests/test_views.py ............
mad/users/tests/test_views.py ..

----------- coverage: platform linux, python 3.5.3-final-0 -----------
Name                          Stmts   Miss  Cover   Missing
-----------------------------------------------------------
mad/base/views.py                 4      0   100%   
mad/builds/admin.py               5      0   100%   
mad/builds/filters.py             7      0   100%   
mad/builds/models.py             78      0   100%   
mad/builds/permissions.py         4      0   100%   
mad/builds/serializers.py        46      0   100%   
mad/builds/tasks.py              10      7    30%   7-16
mad/builds/views.py              64      0   100%   
mad/consumers.py                  4      0   100%   
mad/downloads/models.py           9      0   100%   
mad/projects/admin.py             8      0   100%   
mad/projects/fields.py           41      0   100%   
mad/projects/models.py           46      0   100%   
mad/projects/permissions.py      17      0   100%   
mad/projects/serializers.py      57      0   100%   
mad/projects/views.py            12      0   100%   
mad/urls.py                       9      0   100%   
mad/users/views.py               10      0   100%   
-----------------------------------------------------------
TOTAL                           431      7    98%   

the content of pytest.ini:

[pytest]                                                                                                                                                                                                                                                                        
DJANGO_SETTINGS_MODULE = config.settings.tests                                                                                                                                                                                                                                  
python_functions = test_*                                                                                                                                                                                                                                                       
python_files = test_*                                                                                                                                                                                                                                                           
python_classes = *Tests                                                                                                                                                                                                                                                         
addopts = --poo --reuse-db -s --cov mad --cov-report=term-missing                                                                                                                                                                                                               
norecursedirs = node_modules requirements web_client .git config venv 

[ucyo]

I'm getting the same error, if I use pytest-xdist and the --looponfail option

[fayazkhan]

Here's the most minimal setup for reproducing this error:

$ pip freeze
apipkg==1.4
coverage==4.4.1
execnet==1.4.1
pkg-resources==0.0.0
py==1.4.34
pytest==3.2.1
pytest-cov==2.5.1
pytest-forked==0.2
pytest-xdist==1.20.0

Empty file a.py.

test.py with contents:

import a

Run:

$ py.test test.py --cov=a -f
============================= test session starts ==============================
platform linux -- Python 3.6.2, pytest-3.2.1, py-1.4.34, pluggy-0.4.0
rootdir: /home/fayaz/Programming, inifile:
plugins: xdist-1.20.0, forked-0.2, cov-2.5.1
collected 0 items
collected 0 items


----------- coverage: platform linux, python 3.6.2-final-0 -----------
Name    Stmts   Miss  Cover
---------------------------
a.py        0      0   100%

=============================== warnings summary ===============================
None
  Module already imported so can not be re-written: pytest_cov

-- Docs: http://doc.pytest.org/en/latest/warnings.html
========================== 1 warnings in 0.01 seconds ==========================
############################################################## waiting for changes ###############################################################
### Watching:   /home/fayaz/Programming

[blueyed]

@nicoddemus
Can the internal warning be filtered after all?
It gets emitted in https://github.com/pytest-dev/pytest/blob/3ed8e28ef31004d64ad992a914775fe3ff23b7cb/src/_pytest/assertion/rewrite.py#L202-L205, but then only hooks are called on it (empty in my case):

> …/pytest/src/_pytest/config/__init__.py(601)

 599         def warn(self, code, message, fslocation=None, nodeid=None):                                                                                                                     
 600             """ generate a warning for this test session. """                                                                                                                            
 601  ->         self.hook.pytest_logwarning.call_historic(                                                                                                                                   
 602                 kwargs=dict(                                                                                                                                                             
 603                     code=code, message=message, fslocation=fslocation, nodeid=nodeid                                                                                                     
 604                 )                                                                                                                                                                        
 605             )                                                                                                                                                                            

It looks like this warning is internal, and filters are not applied to it?!

(see also #211)

[nicoddemus]

@blueyed unfortunately, internal warnings were introduced before pytest-warnings was integrated into the core, so they cannot be filtered using standard warning mechanisms. We have plans to update the internal warnings system to use the standard warnings module (pytest-dev/pytest#2452).

The internal warnings can be suppressed from the output with --disable-pytest-warnings only at the moment.