Parallel tests fixes

[thufschmitt]

Fix the issues introduced by #3777

• Restore tests/plugins/libplugintest.* as a dependency of the testsuite
• Shorten the path to the test root to fix a socket path is too long error on the OSX builders

[thufschmitt]

(waiting for the CI to confirm the OSX fix as I can't test it locally)

[Ericson2314]

Maybe we can use relative paths when we create the socket to get around this?

[thufschmitt]

Maybe we can use relative paths when we create the socket to get around this?

I tried that but it's not allowed

I managed to work around the path length by directly putting the daemon socket under $TEST_ROOT in the tests. In theory the error can still happen if $TMPDIR is too long, but that gives us roughly as much margin as what we used to have before.

Now I'm stuck again with a non-sensical error on the OSX builder 😠 (the nix-shell test fails on a call to nix develop, except that I couldn't find any call to nix develop in the whole codebase, so I have no idea where this can come from)

[thufschmitt]

Now I'm stuck again with a non-sensical error on the OSX builder angry

Mh, the same pipeline passed on Tweag's repo (https://github.com/tweag/nix/runs/833213722). I'll try force-pushing to restart the pipeline and see if the failure persists

[edolstra]

Looks like there is also a dependency on tests/config.nix missing: https://nix-cache.s3.amazonaws.com/log/r2qnl4d2k9ix8i2gbi816x6lszmjgf6z-nix-2.4pre7875_5596f879.drv

[thufschmitt]

Looks like there is also a dependency on tests/config.nix missing

Yup', I've also restored it in this branch

The OSX failure now seems to be a real one introduced by 5596f87 (I've tried rebasing it on top of yesterday's master removing the "parallel tests" MR, and it still fails: https://github.com/tweag/nix/runs/833623967)