Disable caching of test results

[taldcroft]

Description

Disable caching of test results to prevent users trying to write into flight directory if tests fail running on installed package.

I think this impacts python setup.py test also (but not 100% sure) but not direct pytest (which doesn't work for namespace packages unfortunately).

Testing

• [N/A] Passes unit tests (no tests)
• Functional testing

Running run_testr as user aldcroft in ska3-shiny on HEAD produces pytest warnings for every unit test because it is trying to write to cache info to /proj/sot/ska3/shiny. I applied this patch as a hot-fix to ska3-shiny on HEAD and confirmed that all those warnings go away and tests still run as expected.

[javierggt]

Hi @taldcroft, I am assuming you read my last comment in PR 21. Wouldn't it be possible to pass this in TESTR_PYTEST_ARGS whenever it is needed?

[taldcroft]

Per my comment in #21, while I'm fine with having environment var hooks for behaviors which can be useful in running package tests, in general I'm thinking of myself and other users that won't know or think about setting them.

The problem of a .cache directory being written into the installed package area is real (when doing import <pkg>; <pkg>.test()). This .cache found its way into the production ska3-flight when running self tests as aca. Not a disaster, but not a good thing.

kady$ pwd
/proj/sot/ska3/flight/lib/python3.6/site-packages
kady$ ls -l .cache/v/cache/lastfailed 
-rw-r--r-- 1 aca aspect 197 May 30 13:50 .cache/v/cache/lastfailed
kady$ cat .cache/v/cache/lastfailed 
{
  "Ska/engarchive/tests/test_comps.py::test_mups_valve": true,
  "Ska/engarchive/tests/test_sync.py::test_sync[cpe1eng]": true,
  "Ska/engarchive/tests/test_sync.py::test_sync[pcad13eng]": true
}

[taldcroft]

This needed to get a basic run_testr passing on HEAD shiny. I confirmed that it works as expected so merging now.