Code emitting warnings

---

examples/test-warn/t/test_add.t

use strict;
use warnings;

use Test::More;

use MyTools qw(add);

plan tests => 4;

is(add(1, 2), 3,   'first');
is(add(2), 2,      'second');
is(add(3), 3,      'third');
is(add(-1, 1), 0,  'fourth');

prove -lv t/test_add.t

Use of uninitialized value $y in addition (+) at /home/gabor/work/slides/perl/examples/test-warn/lib/MyTools.pm line 31.
Use of uninitialized value $y in addition (+) at /home/gabor/work/slides/perl/examples/test-warn/lib/MyTools.pm line 31.
t/test_add.t .. 
1..4
ok 1 - first
ok 2 - second
ok 3 - third
ok 4 - fourth
ok
All tests successful.
Files=1, Tests=4,  0 wallclock secs ( 0.01 usr  0.01 sys +  0.16 cusr  0.02 csys =  0.20 CPU)
Result: PASS