Bug#954763: lintian: Lintian should warn about use of py3versions -i in autopkgtests

[Scott Kitterman <debian@kitterman.com>]

Package: lintian
Version: 2.59.0
Severity: normal

Is recently discussed in a thread on debian-devel [1] there is a common
error in python related auotpkgtests where py3verions -i is used to loop
over 'installed' python3 versions.  This is currently causing a
substantial number of failures since the debci systems testing for the
python3.8 as default transition have python3.7-minimal installed.  This
provides enough of an interpreter to count as being installed (/usr/bin/
python3.7 is present) and to run autopkgtest, but not enough for the
tests themselves to succeed in most cases.

Eventually, this will stop being an immediate problem, so it would be
useful to have lintian detect and warn against it so that these latent
bugs don't accumulate.

Preferably these packages should run their tests with all supported
python3 versions.  This is ensured by including python3-all in the test
dependencies and using py3versions -s (instead of -i).  Tests should run
deterministically, not just based on whatever happens to be installed.

If for some reason a package can't run tests against all supported
versions, then py3versions -d should be used (test against the default
version).

Thanks,

Scott K


[1]  https://lists.debian.org/debian-devel/2020/03/msg00280.html