Do not install tests

[scop]

"Why not" writeup at https://gist.github.com/scop/5910ee85a1352988554e8b8d5d675e65

[jelmer]

While I have sympathy for the argument of not installing tests for disk usage reasons in general, the other arguments listed on that page don't make sense to me:

• there may be no single standard way of running tests; there is no single standard way of invoking other python code once installed either. And while there is no single standard, there are various standards for specifying tests, such as test_suite in setup.cfg, a directory name tests, simply doing test discovery with pytest
• dependencies can be specified with tests_require in setup.cfg, or could e.g. be specified with a "tests" extra
• it's obviously a bad idea to install test code that is not ready for that, but that's just an argument for fixing that or only installing test code that is safe to run

The fact that it's not necessarily easy to run tests out of the box could just be an argument for making it easier.

In this particular case, we're talking about 16k; is that really worth it?