Well, if you don't put any arguments in then $ARGV[0] is undefined. What do you want to do if no arguments are given? Do you want it to cause an error:

unless (@ARGV == 1) {
    die "You must specify one argument\n";
}
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Or do you want to set a default value?

my $argument = $ARGV[0] || 'default' ; # Put your default  
                                       # value here
if ($argument eq 'TEST') {....
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Or do you just want it to ignore the argument?

if (defined $ARGV[0] && $ARGV[0] eq 'TEST') {...
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