When you write test you might have tests cases that pass, but at the same time your code might generate warnings. Some of these warnings might harmless, but other might indicated some problem. Either in the application under test or in the tests.

In addition if someone looks at the output and sees warnings, the person rightly will be worried that there might be issues with the code.

If nothing else then that using it will fill the log files of a web server causing denial of service.

The problem is that a warning does not stop the tests and so new warnings might not be noticed in a CI system.

Of course there are tools to overcome this issue.

You can ask your Test2 based tests to fail if there is any unexpected warning during the test run.

All you need to do is install and import the Test2::Plugin::NoWarnings module.

Let's see an example:

The layout of the files:

.
├── lib
│   └── App.pm
└── t
    ├── 01-test.t
    ├── 02-test.t
    └── 03-test.t

The application under test:

examples/test2-nowarnings/lib/App.pm

package App;
use strict;
use warnings;

sub add {
    my ($x, $y) = @_;

    return $x + $y;
}


1;

Test case with warning

examples/test2-nowarnings/t/01-test.t

use Test2::V0;
use App;

ok( App::add(2), 2 );


done_testing();

prove -l t/01-test.t

t/01-test.t .. Use of uninitialized value $y in addition (+) at .../lib/App.pm line 8.
t/01-test.t .. ok
All tests successful.
Files=1, Tests=1,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.07 cusr  0.00 csys =  0.09 CPU)
Result: PASS

Tests are successful, but there is a warning.

Add Test2::Plugin::NoWarnings to capture warnings

examples/test2-nowarnings/t/02-test.t

use Test2::V0;
use Test2::Plugin::NoWarnings echo => 1;
use App;

ok( App::add(2), 2 );

done_testing();

prove -l t/02-test.t

The results:

t/02-test.t .. 1/? Use of uninitialized value $y in addition (+) at .../lib/App.pm line 8.
# Seeded srand with seed '20190419' from local date.
t/02-test.t .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/2 subtests

Test Summary Report
-------------------
t/02-test.t (Wstat: 256 Tests: 2 Failed: 1)
  Failed test:  1
  Non-zero exit status: 1
Files=1, Tests=2,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.07 cusr  0.00 csys =  0.09 CPU)
Result: FAIL

If we only import the module without the echo parameter it will hide the warning. I think it is much better to show it as it makes it easier to find the source of the problem. Actually it would be even better if we knew in which test-case was the warning generated.

Fixing the warning

In the last example we fixed the test. It does not generate warnings any more and everything is fine with Test2::Plugin::NoWarnings in the code.

examples/test2-nowarnings/t/03-test.t

use Test2::V0;
use Test2::Plugin::NoWarnings echo => 1;
use App;

ok( App::add(2, 0), 2 );

done_testing();

prove -l t/03-test.t

t/03-test.t .. ok
All tests successful.
Files=1, Tests=1,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.07 cusr  0.00 csys =  0.09 CPU)
Result: PASS