Using py.test with compiled library code

Question

I have a python library with the following repository structure:

repobase
 |- mylibrary
 |  |- __init__.py
 |- tests
    |- test_mylibrary.py

Up to now, running the tests could simply be done by calling py.test in the repobase directory. The import mylibrary in test_mylibrary.py then used the local code in repobase/mylibrary.

Now, I've extended the library to use compiled code. Therefore the source code at repobase/mylibrary is not functional on its own. I have to do a setup.py build. This creates repobase/build/lib.linux-x86_64-2.7/mylibrary.

Is there a reasonable way to make py.test use this directory for importing mylibrary? Given these constraints:

1. I do not want to include any sys.path / import magic in test_mylibrary.py because this may break tests in other envrionments.

2. I don't want to give up the possibility to run py.test from repobase. Therefore modifying the PYTHONPATH does not help because . will still be first in sys.path. And thus repobase/mylibrary would be favored over repobase/build/lib.linux-x86_64-2.7/mylibrary.

If not, what's the standard way for testing python libraries, that need building?

Answer 1

I think your problem is simply that py.test is not copying the built shared object to the root of your repository.

I just tried running the UT straight from the Python wiki on testing C extensions using py.test as follows:

python setup.py build
py.test test/examp_unittest.py

This failed with AssertionError: No module named examp.

However, when I follow the wiki to the letter (and run python setup.py test instead), I note that it copies the .so to the root directory (note the last line before it starts running the test):

running test
running egg_info
writing examp.egg-info/PKG-INFO
writing top-level names to examp.egg-info/top_level.txt
writing dependency_links to examp.egg-info/dependency_links.txt
reading manifest file 'examp.egg-info/SOURCES.txt'
writing manifest file 'examp.egg-info/SOURCES.txt'
running build_ext
copying build/lib.linux-x86_64-2.6/examp.so ->
runTest (test.examp_unittest.DeviceTest) ... ok

----------------------------------------------------------------------
Ran 1 test in 0.001s

OK

Having run that on my system, I can now run py.test quite happily on the same code base - as shown below.

============================= test session starts ==============================
platform linux2 -- Python 2.7.3, pytest-2.9.2, py-1.4.31, pluggy-0.3.1
rootdir: /tmp/sotest, inifile: 
collected 1 items 

test/examp_unittest.py .

=========================== 1 passed in 0.01 seconds ===========================

The solution is therefore to copy your shared object to the root of your repository.

To make sure I have run the whole thing from scratch, just building the extension, copying the shared object and then running py.test. This all works as expected.