# foo.t
use strict;
use warnings;

use Test::More qw/no_plan/;
use Test::Exception;

require_ok(q{foo.pl});

Log::Log4perl->appender_thresholds_adjust(7); # disable logging

# ------ negative tests for add() ------
throws_ok { add(); } qr/error/i, q{Expect error when no args};
...

Log::Log4perl->appender_thresholds_adjust(-7); # enable logging

# ------ positive tests for add() ------
cmp_ok(add(2,2), q{==}, 4, q{Expect 2+2=4});

# Note: I want a warning here:
cmp_ok(add(1000,1000), q{==}, 2000, q{Expect 1000+1000=2000});
__END__