I have a slightly different interest in declining to install tests... Arch Linux provides the tests as a split subpackage with currently some hacky shell globbing to delete the tests after make install, then do a second libinstall and delete everything but the tests.
It would be more convenient if we had a Makefile option to install the tests separately.
It's now possible to disable installing tests with a filthy hack: make install TEST_MODULES= TESTSUBDIRS=
However, it's not possible to similarly hack make libinstall LIBSUBDIRS=
Because it installs some toplevel stuff, then runs lib2to3.pgen2.driver on the grammar that got skipped by the LIBSUBDIRS= hack.
Thoughts on maybe splitting this up at install time? Would probably mean duplicating some of libinstall as testinstall...