c.f. https://tox.readthedocs.io/en/latest/ Whether we care about this probably varies a bit; webkitcorepy etc. are in principle installable via pip so testing them via virtualenvs (therefore in isolated environments) would have some value. However, the larger value in my book would be able to run tests against multiple supported Python versions in a single command. That said, this is a relatively small benefit compared with the other benefits many get from it.
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