How about doing it more directly? The obvious solution seems to be to compare against /test|Test|tEst|.../. The glob function will help to create such a pattern:

use strict;
use warnings;

my $pat = "test";
$pat = join "|", glob join "", map { "{".uc.",".lc."}"} split //, $pat
+;
print "$pat\n";

for ( qw( Test test tesT tast ) ) {
    print "$_\n" if /$pat/;
}
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