py.test running Python2 and Python3

Question

I have written a package (http://github.com/anntzer/parsedcmd) that runs with both Python2 and Python3. However, I had to write separate (py.test) unit tests for Python2 and Python3 (mainly because I want to test extra features of Python3, in particular keyword-only arguments), so I have a `test_py2.py` and a `test_py3.py` in a `test` subpackage. Now, if I run, say `py.test2 mypkg`, `test_py2` passes, but `test_py3` fails with a `SyntaxError`. Likewise, for `py.test3 mypkg`, `test_py3` passes but `test_py2` fails (I could make this one work though, it's just an issue of `StringIO` having moved to `io`). I can design the `test` subpackage so that `import mypkg.test` only imports the proper version of the tests, but apparently py.test doesn't care -- it just sees two files matching `test_*` and grabs all tests in both of them, ignoring what `__init__.py` tells him to import. So right now I have to do both `py.test2 mypkg/test/test_py2.py` and `py.test3 mypkg/test/test_py3.py`. Is there…

Accepted Answer

If you can then making your modules importable on all interpreters and skipping tests as appropriate is a common solution. Otherwise you can put the following as "conftest.py" into the test directory:

```
import sys
py3 = sys.version_info[0] >= 3

class DummyCollector(pytest.collect.File):
   def collect(self):
      return []

def pytest_pycollect_makemodule(path, parent):
  bn = path.basename 
  if "py3" in bn and not py3 or ("py2" in bn and py3):
     return DummyCollector(path, parent=parent)
```

This gets picked up a project-specific plugin and will properly ignore a test module with a filename containing a "py2" or "py3" substring on the wrong interpreter version. Of course you can refine it to rather have an explicit list directly in the conftest.py file instead of checking the filename etc.pp.

HTH, holger

py.test running Python2 and Python3

Solution

Problem