This was caused by a combination of changes. When I added pytest as an EUPS package I couldn't believe there was a package called py that I also needed to install so it didn't get an eups package of its own. A while back the conda reference packages were updated in lsstsw/newinstall/Jenkins but not on the shared stack. This wasn't a problem until DM-11693 updated pytest to v3.6.x (matching the new Jekins version).

Adding a py TaP package probably won't be enough because of the setuptools bug that causes it to ignore PYTHONPATH in site.py if there is a version of the package in the system python library. One of the reasons we couldn't update pytest until conda was updated was because the conda version always tended to take priority.

I believe this has been addressed by DM-16129, which provides a new stack containing the w_2018_41 weekly. Eli Rykoff, can you confirm that this fixes your problem?

Hooray!  The new shared stack is able to run scons and pytest as expected.

Brian Van Klaveren is working on the longer term fix in DM-15873 and DM-16163.

Thanks Eli Rykoff!

Honest question: why is this a "Won't Fix"?  It is fixed, right?  Or is the problem that it won't be fixed specifically on w_2018_38?

Well, the real point is that there's no work being done here. I took action (& claimed credit for it) on DM-16129; there's other work ongoing on DM-15873 & DM-16163; nobody is going to come along and do something more to address this ticket specifically.