Write two tests.
my $google = Google::Auth->login(
email => 'test@gmail.com',
password => 'pass',
service => 'cp',
);
isa_ok $google, 'Google::Auth';
my $contactlist = Google::ContactList->fetchall($google);
isa_ok $contactlist, 'Google::ContactList';
Here, I've tested whether these two method calls successfully constructed instances of their classes. I don't know whether these methods are really supposed to be constructors, but at least you can tell what is being tested. The isa_ok function is a handy abbreviation for
ok(
$google->isa('Google::Auth'),
'Constructed an instance of Google::Auth',
);
Then write a few more tests to show that these objects do what they're supposed to do.