coverage.py does not cover script if py.test executes it from another directory

I encountered the same issue when calling “py.test –cov …” from tox. I found a hint on this page: http://blog.ionelmc.ro/2014/05/25/python-packaging/ even though it does not mention this explicitly. Using “–develop” for tox will make sure that coverage data gathering is called from the same directory as coverage analysis.
This section in tox.ini made it work for me to have a test environment for coverage:

[tox]
envlist = ...,py34,cov

[testenv:cov]
# necessary to make cov find the .coverage file
# see http://blog.ionelmc.ro/2014/05/25/python-packaging/
usedevelop = true
commands = py.test --cov=<MODULE_NAME>
deps = pytest pytest-cov