subprocess: output on stderr doesn't mean that a process failed Git sometimes does that. Threading non-determinism did that we sometimes didn't see it, and sometimes we failed.

[tox]
minversion = 1.8
envlist = py{26,27}-pytest

[testenv]
setenv =
    PYTHONHASHSEED = 0
deps =
    pytest: pytest
commands =
    pytest: py.test {posargs}