t: allow skipping expected object ID in ref-store update-ref

We require the caller to pass both the old and new expected object ID to
our `test-tool ref-store update-ref` helper. When trying to update a
symbolic reference though it's impossible to specify the expected object
ID, which means that the test would instead have to force-update the
reference. This is currently impossible though.

Update the helper to optionally skip verification of the old object ID
in case the test passes in an empty old object ID as input.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

t/helper/test-ref-store.c

@@ -298,16 +298,19 @@ static int cmd_update_ref(struct ref_store *refs, const char **argv)
 	const char *new_sha1_buf = notnull(*argv++, "new-sha1");
 	const char *old_sha1_buf = notnull(*argv++, "old-sha1");
 	unsigned int flags = arg_flags(*argv++, "flags", transaction_flags);
-	struct object_id old_oid;
+	struct object_id old_oid, *old_oid_ptr = NULL;
 	struct object_id new_oid;
 
-	if (get_oid_hex(old_sha1_buf, &old_oid))
-		die("cannot parse %s as %s", old_sha1_buf, the_hash_algo->name);
+	if (*old_sha1_buf) {
+		if (get_oid_hex(old_sha1_buf, &old_oid))
+			die("cannot parse %s as %s", old_sha1_buf, the_hash_algo->name);
+		old_oid_ptr = &old_oid;
+	}
 	if (get_oid_hex(new_sha1_buf, &new_oid))
 		die("cannot parse %s as %s", new_sha1_buf, the_hash_algo->name);
 
 	return refs_update_ref(refs, msg, refname,
-			       &new_oid, &old_oid,
+			       &new_oid, old_oid_ptr,
 			       flags, UPDATE_REFS_DIE_ON_ERR);
 }