sub test_init() {

# Set up the environment for running tests.
#
# Hash Parameters:
#
#  * hydra_config: configuration for the Hydra processes for your test.
#
# This clears several environment variables and sets them to ephemeral
# values: a temporary database, temporary Nix store, temporary Hydra
# data directory, etc.
#
# Note: This function must run _very_ early, before nearly any Hydra
# libraries are loaded. To use this, you very likely need to `use Setup`
# and then run `test_init`, and then `require` the Hydra libraries you
# need.
#
# It returns a tuple: a handle to a temporary directory and a handle to
# the postgres service. If either of these variables go out of scope,
# those resources are released and the test environment becomes invalid.
#
# Look at the top of an existing `.t` file to see how this should be used
# in practice.
sub test_init {
    my %opts = @_;

    $ENV{'HYDRA_CONFIG'} = "$dir/hydra.conf";

    open(my $fh, '>', $ENV{'HYDRA_CONFIG'}) or die "Could not open file '" . $ENV{'HYDRA_CONFIG'}. " $!";
    print $fh $opts{'hydra_config'} || "";
    close $fh;