use strict;
use warnings;
use feature 'say';

sub test_function {
    my $ref = shift;    # this function takes one argument, a ref to an ARRAY

    # Note: you could do extra manual checking of function arguments.
    # Not necessarily recommended: shown for educational purposes.
    defined($ref) or die "oops: you did not pass any arguments";
    @_ and die "oops: this function takes exactly one argument";
}

say "Calling test_function with no arguments:";
eval { 
    test_function();
};
say $@;

say "Calling test_function with a single undefined argument:";
eval {
   test_function(undef);
};
say $@;