cleanup: check for None object identity in cases where that is what the 'contract' says Avoid applying bool() on complex objects - it might return something unexpected such as the key (which might be 0 and thus be false). Checking for None is more safe and faster.

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

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