Scroll to navigation

Test::NoWarnings(3) User Contributed Perl Documentation Test::NoWarnings(3)


Test::NoWarnings - Make sure you didn't emit any warnings while testing


For scripts that have no plan

  use Test::More 'no_plan';
  use Test::NoWarnings;

that's it, you don't need to do anything else

For scripts that look like

  use Test::More tests => x;

change to

  use Test::More tests => x + 1;
  use Test::NoWarnings;

For scripts that use done_testing, use:

  use Test::More;
  use Test::NoWarnings 'had_no_warnings';
  ... # your actual tests


In general, your tests shouldn't produce warnings. This modules causes any warnings to be captured and stored. It automatically adds an extra test that will run when your script ends to check that there were no warnings. If there were any warnings, the test will give a "not ok" and diagnostics of where, when and what the warning was, including a stack trace of what was going on when the it occurred.

If some of your tests are supposed to produce warnings then you should be capturing and checking them with Test::Warn, that way Test::NoWarnings will not see them and so not complain.

The test is run by an "END" block in Test::NoWarnings. It will not be run when any forked children exit.


Simply by using the module, you automatically get an extra test at the end of your script that checks that no warnings were emitted. So just stick

  use Test::NoWarnings;

at the top of your script and continue as normal.

If you want more control you can invoke the test manually at any time with "had_no_warnings".

The warnings your test has generated so far are stored in an array. You can look inside and clear this whenever you want with warnings() and "clear_warnings", however, if you are doing this sort of thing then you probably want to use Test::Warn in combination with Test::NoWarnings.

If you have a test script written using done_testing and no test plan, you have to call "had_no_warnings" before you call done_testing.

use vs require

You will almost always want to do

  use Test::NoWarnings;

If you do a "require" rather than a "use", then there will be no automatic test at the end of your script.


If warning is captured during your test then the details will output as part of the diagnostics. You will get:

  • the number and name of the test that was executed just before the warning (if no test had been executed these will be 0 and '')
  • the message passed to "warn",
  • a full dump of the stack when warn was called, courtesy of the "Carp" module

By default, all warning messages will be emitted in one block at the end of your test script.

The :early pragma

One common complaint from people using Test::NoWarnings is that all of the warnings are emitted in one go at the end. While this is the safest and most correct time to emit these diagnostics, it can make debugging these warnings difficult.

As of Test::NoWarnings 1.04 you can provide an experimental ":early" pragma when loading the module to force warnings to be thrown via diag at the time that they actually occur.

  use Test::NoWarnings ':early';

As this will cause the diag to be emitted against the previous test and not the one in which the warning actually occurred it is recommended that the pragma be turned on only for debugging and left off when not needed.



This checks that there have been warnings emitted by your test scripts. Usually you will not call this explicitly as it is called automatically when your script finishes.


This will clear the array of warnings that have been captured. If the array is empty then a call to had_no_warnings() will produce a pass result.


This will return the array of warnings captured so far. Each element of this array is an object containing information about the warning. The following methods are available on these object.

  • $warn->getMessage

    Get the message that would been printed by the warning.

  • $warn->getCarp

    Get a stack trace of what was going on when the warning happened, this stack trace is just a string generated by the Carp module.

  • $warn->getTrace

    Get a stack trace object generated by the Devel::StackTrace module. This will return undef if Devel::StackTrace is not installed.

  • $warn->getTest

    Get the number of the test that executed before the warning was emitted.

  • $warn->getTestName

    Get the name of the test that executed before the warning was emitted.


When counting your tests for the plan, don't forget to include the test that runs automatically when your script ends.

Checking for warnings is done using $SIG{__WARN__}. If other modules use this hook, it can interfere with this module's operation. For example, using the Carp::Always module will cause this module to always report no warnings.


Bugs should be reported via the CPAN bug tracker at


For other issues, contact the author.


This was previously known as Test::Warn::None


Test::Builder, Test::Warn


Fergal Daly <>

Adam Kennedy <>


Copyright 2003 - 2007 Fergal Daly.

Some parts copyright 2010 - 2011 Adam Kennedy.

This program is free software and comes with no warranty. It is distributed under the LGPL license

See the file LICENSE included in this distribution or

2021-07-28 perl v5.38.2