use Test::Taint tests=>4;
taint_checking_ok();        # We have to have taint checking on
my $id = "deadbeef";        # Dummy session ID
taint( $id );               # Simulate it coming in from the web
tainted_ok( $id );
$id = validate_id( $id );   # Your routine to check the $id
untainted_ok( $id );        # Did it come back clean?
ok( defined $id );