Sadly the NixOS tests I've written fail in my Hydra instance and I don't know why. I'll wait and see if anyone answers in the NixOS channel first, then re-post here in full detail. In essence all my tests use a postgresql service which after some time leads to

machine # [  336.433468] postgresql-pre-start[896]: Success. You can now start the database server using:
machine # [  336.452698] postgresql-pre-start[896]:     /nix/store/6cn4h4icjjvg9yqx8iy55hvmqbq0jj2j-postgresql-10.21/bin/pg_ctl -D /var/lib/postgresql/10.0 -l logfile start
machine # [  337.181043] systemd[1]: postgresql.service: Failed with result 'timeout'.

In reply to @roberthensing:matrix.org
evaluation hasn't started for 13h; seems like something is wrong https://hydra.nixos.org/jobset/nixos/trunk-combined