use warnings;
use strict;
use feature qw/ say /;
use Data::Dumper;
$Data::Dumper::Indent = 0;

sub test_function {
    my $ref_array = @_;
    say Dumper (@_); # $VAR1 = [[1,2,3],[4,5,6]];
    say scalar @{ $ref_array }; # line 12
}

my @test_array = ([1, 2, 3], [4, 5, 6]);
&test_function(\@test_array);