Test2::Manual::Testing::Introduction - Introduction to testing with Test2.


This tutorial is a beginners introduction to testing. This will take you through writing a test file, making assertions, and running your test.



Test files typically are placed inside the t/ directory, and end with the .t file extension.


use Test2::V0;

# Assertions will go here


This is all the boilerplate you need.

use Test2::V0;

This loads a collection of testing tools that will be described later in the tutorial. This will also turn on strict and warnings for you.


This should always be at the end of your test files. This tells Test2 that you are done making assertions. This is important as test2 will assume the test did not complete successfully without this, or some other form of test "plan".


You should always list bundles and tools directly. You should not simply list Test2::Suite and call it done, bundles and tools may be moved out of Test2::Suite to their own dists at any time.


[Prereqs / TestRequires]
Test2::V0 = 0.000060


my %WriteMakefileArgs = (
    "Test2::V0" => "0.000060"


test_requires 'Test2::V0' => '0.000060';


my $build = Module::Build->new(
    test_requires => {
        "Test2::V0" => "0.000060",


The most simple tool for making assertions is ok(). ok() lets you assert that a condition is true.

ok($CONDITION, "Description of the condition");

Here is a complete t/example.t:

use Test2::V0;

ok(1, "1 is true, so this will pass");



Test files are simply scripts. Just like any other script you can run the test directly with perl. Another option is to use a test "harness" which runs the test for you, and provides extra information and checks the scripts exit value for you.


$ perl -Ilib t/example.t

Which should produce output like this:

# Seeded srand with seed '20161028' from local date.
ok 1 - 1 is true, so this will pass

If the test had failed (ok(0, ...)) it would look like this:

# Seeded srand with seed '20161028' from local date.
not ok 1 - 0 is false, so this will fail

Test2 will also set the exit value of the script, a successful run will have an exit value of 0, a failed run will have a non-zero exit value.


The yath command line tool is provided by Test2::Harness which you may need to install yourself from cpan. yath is the harness written specifically for Test2.

$ yath -Ilib t/example.t

This will produce output similar to this:

( PASSED )  job  1    t/example.t


Run ID: 1508027909

All tests were successful!

You can also request verbose output with the -v flag:

$ yath -Ilib -v t/example.t

Which produces:

( LAUNCH )  job  1    example.t
(  NOTE  )  job  1    Seeded srand with seed '20171014' from local date.
[  PASS  ]  job  1  + 1 is true, so this will pass
[  PLAN  ]  job  1    Expected asserions: 1
( PASSED )  job  1    example.t


Run ID: 1508028002

All tests were successful!


The prove command line tool is provided by the Test::Harness module which comes with most versions of perl. Test::Harness is dual-life, which means you can also install the latest version from cpan.

$ prove -Ilib t/example.t

This will produce output like this:

example.t .. ok
All tests successful.
Files=1, Tests=1,  0 wallclock secs ( 0.01 usr  0.00 sys +  0.05 cusr  0.00 csys =  0.06 CPU)
Result: PASS

You can also request verbose output with the -v flag:

$ prove -Ilib -v t/example.t

The verbose output looks like this:

example.t ..
# Seeded srand with seed '20161028' from local date.
ok 1 - 1 is true, so this will pass
All tests successful.
Files=1, Tests=1,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.06 cusr  0.00 csys =  0.08 CPU)
Result: PASS


All tests need a "plan". The job of a plan is to make sure you ran all the tests you expected. The plan prevents a passing result from a test that exits before all the tests are run.

There are 2 primary ways to set the plan:


The most common, and recommended way to set a plan is to add done_testing at the end of your test file. This will automatically calculate the plan for you at the end of the test. If the test were to exit early then done_testing would not run and no plan would be found, forcing a failure.


The plan() function allows you to specify an exact number of assertions you want to run. If you run too many or too few assertions then the plan will not match and it will be counted as a failure. The primary problem with this way of planning is that you need to add up the number of assertions, and adjust the count whenever you update the test file.

plan() must be used before all assertions, or after all assertions, it cannot be done in the middle of making assertions.


The Test2::V0 bundle provides a lot more than ok(), plan(), and done_testing(). The biggest tools to note are:

is($a, $b, $description)

is() allows you to compare 2 structures and insure they are identical. You can use it for simple string comparisons, or even deep data structure comparisons.

is("foo", "foo", "Both strings are identical");

is(["foo", 1], ["foo", 1], "Both arrays contain the same elements");
like($a, $b, $description)

like() is similar to is() except that it only checks items listed on the right, it ignores any extra values found on the left.

like([1, 2, 3, 4], [1, 2, 3], "Passes, the extra element on the left is ignored");

You can also used regular expressions on the right hand side:

like("foo bar baz", qr/bar/, "The string matches the regex, this passes");

You can also nest the regexes:

like([1, 2, 'foo bar baz', 3], [1, 2, qr/bar/], "This passes");


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.