Test2::Manual::Tooling::Testing - Tutorial on how to test your testing tools.


Testing your test tools used to be a complex and difficult prospect. The old tools such as Test::Tester and Test::Builder::Tester were limited, and fragile. Test2 on the other hand was designed from the very start to be easily tested! This tutorial shows you how.


The key to making Test2 easily testable (specially when compared to Test::Builder) is the intercept function.

use Test2::API qw/intercept/;

my $events = intercept {
    ok(1, "pass");
    ok(0, "fail");

    diag("A diag");

The intercept function lets you use any test tools you want inside a codeblock. No events or contexts generated within the intercept codeblock will have any effect on the outside testing state. The intercept function completely isolates the tools called within.

Note: Plugins and things that effect global API state may not be fully isolated. intercept is intended specifically for event isolation.

The intercept function will return an arrayref containing all the events that were generated within the codeblock. You can now make any assertions you want about the events you expected your tools to generate.

    bless({...}, 'Test2::Event::Ok'),   # pass
    bless({...}, 'Test2::Event::Ok'),   # fail
    bless({...}, 'Test2::Event::Diag'), # Failure diagnostics (not always a second event)
    bless({...}, 'Test2::Event::Diag'), # custom 'A diag' message

Most test tools eventually produce one or more events. To effectively verify the events you get from intercept you really should read up on how events work Test2::Manual::Anatomy::Event. Once you know about events you can move on to the next section which points you at some helpers.



This is the most recent set of tools to help you test your events. To really understand these you should familiarize yourself with Test2::Manual::Anatomy::Event. If you are going to be writing anything more than the most simple of tools you should know how events work.

The Test2::Tools::Tester documentation is a good place for further reading.


The Test2::Tools::HarnessTester can export the summarize_events() tool. This tool lets you run your event arrayref through Test2::Harness so that you can get a pass/fail summary.

my $summary = summarize_events($events);

The summary looks like this:

    plan       => $plan_facet,         # the plan event facet
    pass       => $bool,               # true if the events result in a pass
    fail       => $bool,               # true if the events result in a fail
    errors     => $error_count,        # Number of error facets seen
    failures   => $failure_count,      # Number of failing assertions seen
    assertions => $assertion_count,    # Total number of assertions seen


DEPRECATED These tools were written before the switch to faceted events. These will still work, but are no longer the recommended way to test your tools.

The Test2::Tools::Compare library exports a handful of extras to help test events.

event $TYPE => ...

Use in an array check against $events to check for a specific type of event with the properties you specify.

fail_events $TYPE => ...

Use when you expect a failing assertion of $TYPE. This will automatically check that the next event following it is a diagnostics message with the default failure text.

Note: This is outdated as a single event may now possess both the failing assertion AND the failing text, such events will fail this test.


Test2::Manual - Primary index of the manual.


The source code repository for Test2-Manual can be found at


Chad Granum <>


Chad Granum <>


Copyright 2018 Chad Granum <>.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.