Make test-path-utils more robust against incorrect use

Previously, this test utility happily returned with exit code 0 if garbage
was thrown at it. Now it reports failure if an unknown function name was
given on the command line.
Signed-off-by: NJohannes Sixt <j6t@kdbg.org>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

test-path-utils.c

@@ -7,6 +7,7 @@ int main(int argc, char **argv)
 		int rv = normalize_absolute_path(buf, argv[2]);
 		assert(strlen(buf) == rv);
 		puts(buf);
+		return 0;
 	}
 
 	if (argc >= 2 && !strcmp(argv[1], "make_absolute_path")) {
@@ -15,12 +16,16 @@ int main(int argc, char **argv)
 			argc--;
 			argv++;
 		}
+		return 0;
 	}
 
 	if (argc == 4 && !strcmp(argv[1], "longest_ancestor_length")) {
 		int len = longest_ancestor_length(argv[2], argv[3]);
 		printf("%d\n", len);
+		return 0;
 	}
 
-	return 0;
+	fprintf(stderr, "%s: unknown function name: %s\n", argv[0],
+		argv[1] ? argv[1] : "(there was none)");
+	return 1;
 }