pytest-postgresql in nix in docker

We use GitLab CI and Nix for our projects. For Python projects too. And we use pytest for Python projects. And when we use PostgreSQL, we use pytest-postgresql. Therefore, somewhere in our .gitlab-ci.yml, there is something like:

test:
  image: nixos/nix
  script:
    - nix develop -c pytest

If you don’t see imediately why tests must fail, I offer the single of about 22 thousands of logged lines:

pg_ctl: cannot be run as root

I’ve spent two days trying to find out how to persuade nixos/nix to let me run pytest under non-root. I offer you the following:

test:
  image: nixos/nix
  script: |
    nix profile install nixpkgs#su
    mkdir /etc/pam.d
    echo 'auth sufficient pam_rootok.so' > /etc/pam.d/su
    echo 'account required pam_permit.so' >> /etc/pam.d/su
    echo 'session required pam_permit.so' >> /etc/pam.d/su
    echo "user::1000:1000::/var/empty:$(cat /etc/passwd | grep root | cut -d':' -f7)" >> /etc/passwd
    nix develop -c su -c pytest user

Please, note that we don’t need to run nix develop as non-root, which is completely different problem.