You can run Hydra's test suite with the following:
    [nix-shell]$ make check
    [nix-shell]$ # to run as many tests as you have cores:
    [nix-shell]$ make check YATH_JOB_COUNT=$NIX_BUILD_CORES
    [nix-shell]$ # or run yath directly:
    [nix-shell]$ yath test
    [nix-shell]$ # to run as many tests as you have cores:
    [nix-shell]$ yath test -j $NIX_BUILD_CORES
When using `yath` instead of `make check`, ensure you have run `make`
in the root of the repository at least once.
**Warning**: Currently, the tests can fail
if run with high parallelism [due to an issue in
`Test::PostgreSQL`](https://github.com/TJC/Test-postgresql/issues/40)
causing database ports to collide.