test.libregrtest is not installed, which breaks running of test suite from installed Python.
Probably LIBSUBDIRS in Makefile.pre.in should be updated.

$ python3.5 -m test test_int
[1/1] test_int
1 test OK.
$ python3.6 -m test test_int
Traceback (most recent call last):
  File "/usr/lib64/python3.6/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib64/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/lib64/python3.6/test/__main__.py", line 1, in <module>
    from test import regrtest
  File "/usr/lib64/python3.6/test/regrtest.py", line 14, in <module>
    from test.libregrtest import main, main_in_temp_cwd
ImportError: No module named 'test.libregrtest'

New changeset 1f563b259f09 by Victor Stinner in branch 'default':
Issue #25694: Install test.libregrtest to be able to run tests on the installed
https://hg.python.org/cpython/rev/1f563b259f09

New changeset fea86d0049d2 by Victor Stinner in branch 'default':
Issue #25694: Fix test_regrtest for installed Python
https://hg.python.org/cpython/rev/fea86d0049d2

Hum, not only libregrtest was not installable, but test_regrtest didn't work on installed Python.

Can you please retry?

It would be nice to modify test_regrtest to *not* write into the test package, but I failed to find a way to load tests from a different directory :-/

It used to be there were also changes that needed to be made to the windows build files when a new directory was added.  Nosying Steve in case this is still true, assuming there is an option to install the tests (which there might not be, I have no idea not being a Windows user).

R. David Murray added the comment:
> It used to be there were also changes that needed to be made to the windows build files when a new directory was added.  Nosying Steve in case this is still true, assuming there is an option to install the tests (which there might not be, I have no idea not being a Windows user).

I failed to find other test subdirectories in PCbuild/ :-/ I don't
think that tests are installed or installable on Windows.

Thanks. For 3.5 and later we automatically grab Lib/**/* (except *.py[co]), with Lib/test/**/* split out into a separate install option.

I disliked the manual updating as much as everyone else did :)

Thanks for doing that, Steve.  It would be lovely to fix the unix make too, but I'm sure there's a reason why it is currently done the way it is done and I don't feel like figuring out why so as to try to make things better :)

@Victor - is there anything else to be done for this issue or can we close it?

Please close the issue.