hydra-update-gc-roots: add a very basic test validating successful execution

t/scripts/hydra-update-gc-roots/update-gc-roots.t

@@ -0,0 +1,22 @@
+use feature 'unicode_strings';
+use strict;
+use warnings;
+use Setup;
+use Test2::V0;
+
+my $ctx = test_context();
+my $builds = $ctx->makeAndEvaluateJobset(
+    expression => "one-job.nix",
+    build => 1
+);
+
+subtest "Updating GC roots" => sub {
+    my ($res, $stdout, $stderr) = captureStdoutStderr(5, ("hydra-update-gc-roots"));
+    is($res, 0, "hydra-update-gc-roots should exit zero");
+    if ($res != 0) {
+        print "gc roots stdout: $stdout\n";
+        print "gc roots stderr: $stderr";
+    }
+};
+
+done_testing;