Getopt::Long will not exit for you; it will warn you (and the user) about the error, but it's up to you to exit if there was a problem.

Be sure to check the return value from GetOptions:

use Getopt::Long;

my $option_test;
my $result = GetOptions ( 'test=s' => \$option_test );

if (! $result) {
    die "Invalid option specifications";
}
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Example:

$ ./getopt.pl -t
Option test requires an argument
Invalid option specifications at ./getopt.pl line 9.
$
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