internal/pkg: write per-artifact logs

This is currently only used by execArtifact. A later patch will add additional logging facilities.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg_test.go

@@ -314,6 +314,11 @@ func checkWithCache(t *testing.T, testCases []cacheTestCase) {
 				t.Fatal(err)
 			}
 
+			// destroy non-deterministic status files
+			if err := os.RemoveAll(base.Append("status").String()); err != nil {
+				t.Fatal(err)
+			}
+
 			var checksum pkg.Checksum
 			if err := pkg.HashDir(&checksum, base); err != nil {
 				t.Fatalf("HashDir: error = %v", err)
@@ -382,6 +387,9 @@ func cureMany(t *testing.T, c *pkg.Cache, steps []cureStep) {
 		} else if step.pathname != ignorePathname && !pathname.Is(step.pathname) {
 			t.Fatalf("Cure: pathname = %q, want %q", pathname, step.pathname)
 		} else if checksum != makeChecksumH(step.checksum) {
+			if checksum == (unique.Handle[pkg.Checksum]{}) {
+				checksum = unique.Make(pkg.Checksum{})
+			}
 			t.Fatalf(
 				"Cure: checksum = %s, want %s",
 				pkg.Encode(checksum.Value()), pkg.Encode(step.checksum),