Regression test for recent fixed output derivation bug

It turns out that the hydra test suite was not testing fixed output
derivations at all!

I tested that this test fails before the fix, and suceeds after.

Also, delete a generated file that I accidentally committed by mistake
when moving things around.

Author: Ericson2314

subprojects/hydra-tests/jobs/config.nix

@@ -0,0 +1,3 @@
+#! /bin/sh
+
+echo -n hello > $out

subprojects/hydra-tests/jobs/fod-builder.sh

@@ -0,0 +1,13 @@
+with import ./config.nix;
+{
+  # A flat-hash fixed-output derivation.
+  # sha256 of "hello" (no newline).
+  fod = derivation {
+    name = "test-fod";
+    system = builtins.currentSystem;
+    builder = ./fod-builder.sh;
+    outputHashMode = "flat";
+    outputHashAlgo = "sha256";
+    outputHash = "2cf24dba5fb0a30e26e83b2ac5b9e29e1b161e5c1fa7425e73043362938b9824";
+  };
+}

subprojects/hydra-tests/jobs/fod.nix

@@ -0,0 +1,28 @@
+use strict;
+use warnings;
+use Setup;
+use Test2::V0;
+
+# Regression test for the harmonia-store-core bug fixed in 2f09d76:
+# a missing trailing colon in the FOD fingerprint
+# "fixed:out:<hashAlgo>:<hex>:" caused output_paths() to compute wrong
+# store paths for fixed-output derivations.
+
+my $ctx = test_context();
+
+my $builds = $ctx->makeAndEvaluateJobset(
+    expression => "fod.nix",
+    build => 1,
+);
+
+subtest "FOD build succeeds with correct output path" => sub {
+    my $build = $builds->{"fod"};
+    is($build->finished, 1, "Build should be finished.");
+    is($build->buildstatus, 0, "Build should have succeeded.");
+
+    my $out = $build->buildoutputs->find({ name => "out" });
+    ok(defined $out, "Build should have an 'out' output");
+    like($out->path, qr|/nix/store/|, "Output path should be a store path");
+};
+
+done_testing;