PyTest doesn't run any tests

PyTest doesn't run any tests, and it's not clear why. I tried using -debug but didn't get any valuable information. It's not clear how to debug problems like this with pytest (looks like some kind of problem with PyTest config settings / env variables / test names?)

Sample test file:

$ cat test_sanity.py 
import pytest


@pytest.mark.sanity
def test_me():
    """ I'm a test. """

    assert True

      

        
        
        
      

    

But PyTest doesn't run any test:

$ pytest
================================================== test session starts ===================================================
platform linux2 -- Python 2.7.12, pytest-3.1.3, py-1.4.34, pluggy-0.4.0
rootdir: /home/qawizard/pytest-hell, inifile:
plugins: xdist-1.15.0, timeout-1.2.0
collected 1 item s

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Exit: Done! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
============================================== no tests ran in 0.13 seconds ==============================================

      

        
        
        
      

    

Why is that?