is(scalar grep(/\A\Q$x[0]\E\z/, @f), 1, 'old file still there');
my @new = grep(!/\A\Q$x[0]\E\z/, @f);
is(scalar @new, 1, '1 new file written (b4dc0ffee skipped)');
is(scalar grep(/\A\Q$x[0]\E\z/, @f), 1, 'old file still there');
my @new = grep(!/\A\Q$x[0]\E\z/, @f);
is(scalar @new, 1, '1 new file written (b4dc0ffee skipped)');