+is(PublicInbox::Hval::to_filename(''), undef, 'empty string returns undef');
+
+my $s = "\0\x07\n";
+PublicInbox::Hval::src_escape($s);
+is($s, "\\0\\a\n", 'src_escape works as intended');
+
+foreach my $s ('Hello/World.pm', 'Zcat', 'hello world.c', 'Eléanor', '$at') {
+ my $attr = to_attr($s);
+ is(from_attr($attr), $s, "$s => $attr => $s round trips");
+}
+
+{
+ my $bad = to_attr('foo//bar');
+ ok(!$bad, 'double-slash rejected');
+}