Expanding on diotalevi's solution, to allow for the case where $test may be mixed-case, I would write:

use strict;
my $test="yes";
print "test=$test\n";
if ("\L$test" eq "yes") { # No need to L-case the constant
  print "yes\n";
}else{
  print "no\n";
}
[download]

Anyhow I'd prefer to use the reqular-expression match, as indicated by pzbagel.