#!/usr/bin/perl -w
use strict;

/^t(?!est\b)\w*t$/ and print while <DATA>;

__DATA__
test
testset
tot
tesset
tt

##</code><code>##

#!/usr/bin/perl -lw
use strict;

$_ = "thought test tot 1 2 3 tesset";

s/t(?!est\b)\w*t\s*//g;

print;