A good module to start your tests with is
Test::Device::SerialPort.
For example:
#!/usr/bin/perl -l
use strict;
use warnings;
use Test::Device::SerialPort qw( :STAT 0.05 );
use Data::Dumper::Concise;
use Test::More;
plan tests => 13;
my $cfgname = "tpj4.cfg";
Test::Device::SerialPort->set_test_mode_active(1);
my $ob = Test::Device::SerialPort->new('COM7');
die unless ($ob);
ok( $ob->user_msg(1), 'user_msg on' );
ok( $ob->error_msg(1), 'error_msg on' );
ok( $ob->can_baud, 'can_baud' );
ok( $ob->can_databits, 'can databits' );
ok( $ob->can_parity_enable, 'can parity_enable' );
ok( scalar $ob->debug("T"), 'T' );
ok( scalar $ob->debug(), 'read debug state' );
ok( $ob->can_stopbits(1), 'can_stopbits' );
ok( $ob->can_handshake("rts"), 'set can_handshake' );
ok( $ob->write_settings, 'write settings' );
ok( $ob->save($cfgname), 'save settings' );
ok( $ob->write("AT&V\r") );
my ($result1) = $ob->input;
print Dumper ("result = $result1");
ok( $ob->write("AT+CGDCONT?") );
my ($result2) = $ob->input;
print Dumper ("result = $result2");
undef $ob;