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Test::Builder - Backend for building test libraries


package My::Test::Module;
use base 'Test::Builder::Module';

my $CLASS = __PACKAGE__;

sub ok {
    my($test, $name) = @_;
    my $tb = $CLASS->builder;

    $tb->ok($test, $name);


Test::Simple and Test::More have proven to be popular testing modules, but they're not always flexible enough. Test::Builder provides a building block upon which to write your own test libraries which can work together.


my $Test = Test::Builder->new;

Returns a Test::Builder object representing the current state of the test.

Since you only run one test per program new always returns the same Test::Builder object. No matter how many times you call new(), you're getting the same object. This is called a singleton. This is done so that multiple modules share such global information as the test counter and where test output is going.

If you want a completely new Test::Builder object different from the singleton, use create.

my $Test = Test::Builder->create;

Ok, so there can be more than one Test::Builder object and this is how you get it. You might use this instead of new() if you're testing a Test::Builder based module, but otherwise you probably want new.

NOTE: the implementation is not complete. level, for example, is still shared amongst all Test::Builder objects, even ones created using this method. Also, the method name may change in the future.

my $child = $builder->child($name_of_child);
$child->plan( tests => 4 );

Returns a new instance of Test::Builder. Any output from this child will be indented four spaces more than the parent's indentation. When done, the finalize method must be called explicitly.

Trying to create a new child with a previous child still active (i.e., finalize not called) will croak.

Trying to run a test when you have an open child will also croak and cause the test suite to fail.

$builder->subtest($name, \&subtests);

See documentation of subtest in Test::More.

my $ok = $child->finalize;

When your child is done running tests, you must call finalize to clean up and tell the parent your pass/fail status.

Calling finalize on a child with open children will croak.

If the child falls out of scope before finalize is called, a failure diagnostic will be issued and the child is considered to have failed.

No attempt to call methods on a child after finalize is called is guaranteed to succeed.

Calling this on the root builder is a no-op.

if ( my $parent = $builder->parent ) {

Returns the parent Test::Builder instance, if any. Only used with child builders for nested TAP.

diag $builder->name;

Returns the name of the current builder. Top level builders default to $0 (the name of the executable). Child builders are named via the child method. If no name is supplied, will be named "Child of $parent->name".


Reinitializes the Test::Builder singleton to its original state. Mostly useful for tests run in persistent environments where the same test might be run multiple times in the same process.

Setting up tests

These methods are for setting up tests and declaring how many there are. You usually only want to call one of these methods.

$Test->plan( skip_all => $reason );
$Test->plan( tests => $num_tests );

A convenient way to set up your tests. Call this and Test::Builder will print the appropriate headers and take the appropriate actions.

If you call plan(), don't call any of the other methods below.

If a child calls "skip_all" in the plan, a Test::Builder::Exception is thrown. Trap this error, call finalize() and don't run any more tests on the child.

my $child = $Test->child('some child');
eval { $child->plan( $condition ? ( skip_all => $reason ) : ( tests => 3 )  ) };
if ( eval { $@->isa('Test::Builder::Exception') } ) {
# run your tests
my $max = $Test->expected_tests;

Gets/sets the number of tests we expect this test to run and prints out the appropriate headers.


Declares that this test will run an indeterminate number of tests.


Declares that you are done testing, no more tests will be run after this point.

If a plan has not yet been output, it will do so.

$num_tests is the number of tests you planned to run. If a numbered plan was already declared, and if this contradicts, a failing test will be run to reflect the planning mistake. If no_plan was declared, this will override.

If done_testing() is called twice, the second call will issue a failing test.

If $num_tests is omitted, the number of tests run will be used, like no_plan.

done_testing() is, in effect, used when you'd want to use no_plan, but safer. You'd use it like so:

$Test->ok($a == $b);

Or to plan a variable number of tests:

for my $test (@tests) {
$plan = $Test->has_plan

Find out whether a plan has been defined. $plan is either undef (no plan has been set), no_plan (indeterminate # of tests) or an integer (the number of expected tests).


Skips all the tests, using the given $reason. Exits immediately with 0.

my $pack = $Test->exported_to;

Tells Test::Builder what package you exported your functions to.

This method isn't terribly useful since modules which share the same Test::Builder object might get exported to different packages and only the last one will be honored.

Running tests

These actually run the tests, analogous to the functions in Test::More.

They all return true if the test passed, false if the test failed.

$name is always optional.

$Test->ok($test, $name);

Your basic test. Pass if $test is true, fail if $test is false. Just like Test::Simple's ok().

$Test->is_eq($got, $expected, $name);

Like Test::More's is(). Checks if $got eq $expected. This is the string version.

undef only ever matches another undef.

$Test->is_num($got, $expected, $name);

Like Test::More's is(). Checks if $got == $expected. This is the numeric version.

undef only ever matches another undef.

$Test->isnt_eq($got, $dont_expect, $name);

Like Test::More's isnt(). Checks if $got ne $dont_expect. This is the string version.

$Test->isnt_num($got, $dont_expect, $name);

Like Test::More's isnt(). Checks if $got ne $dont_expect. This is the numeric version.

$Test->like($this, qr/$regex/, $name);
$Test->like($this, '/$regex/', $name);

Like Test::More's like(). Checks if $this matches the given $regex.

$Test->unlike($this, qr/$regex/, $name);
$Test->unlike($this, '/$regex/', $name);

Like Test::More's unlike(). Checks if $this does not match the given $regex.

$Test->cmp_ok($this, $type, $that, $name);

Works just like Test::More's cmp_ok().

$Test->cmp_ok($big_num, '!=', $other_big_num);

Other Testing Methods

These are methods which are used in the course of writing a test but are not themselves tests.


Indicates to the Test::Harness that things are going so badly all testing should terminate. This includes running any additional test scripts.

It will exit with 255.


Skips the current test, reporting $why.


Like skip(), only it will declare the test as failing and TODO. Similar to

print "not ok $tnum # TODO $why\n";

Test building utility methods

These methods are useful when writing your own test methods.


This method used to be useful back when Test::Builder worked on Perls before 5.6 which didn't have qr//. Now its pretty useless.

Convenience method for building testing functions that take regular expressions as arguments.

Takes a quoted regular expression produced by qr//, or a string representing a regular expression.

Returns a Perl value which may be used instead of the corresponding regular expression, or undef if its argument is not recognised.

For example, a version of like(), sans the useful diagnostic messages, could be written as:

sub laconic_like {
    my ($self, $this, $regex, $name) = @_;
    my $usable_regex = $self->maybe_regex($regex);
    die "expecting regex, found '$regex'\n"
        unless $usable_regex;
    $self->ok($this =~ m/$usable_regex/, $name);
my $is_fh = $Test->is_fh($thing);

Determines if the given $thing can be used as a filehandle.

Test style


How far up the call stack should $Test look when reporting where the test failed.

Defaults to 1.

Setting $Test::Builder::Level overrides. This is typically useful localized:

sub my_ok {
    my $test = shift;

    local $Test::Builder::Level = $Test::Builder::Level + 1;

To be polite to other functions wrapping your own you usually want to increment $Level rather than set it to a constant.


Whether or not the test should output numbers. That is, this if true:

ok 1
ok 2
ok 3

or this if false


Most useful when you can't depend on the test output order, such as when threads or forking is involved.

Defaults to on.


If set true no diagnostics will be printed. This includes calls to diag().


Normally, Test::Builder does some extra diagnostics when the test ends. It also changes the exit code as described below.

If this is true, none of that will be done.


If set to true, no "1..N" header will be printed.


Controlling where the test output goes.

It's ok for your test to change where STDOUT and STDERR point to, Test::Builder's default output settings will not be affected.


Prints out the given @msgs. Like print, arguments are simply appended together.

Normally, it uses the failure_output() handle, but if this is for a TODO test, the todo_output() handle is used.

Output will be indented and marked with a # so as not to interfere with test output. A newline will be put on the end if there isn't one already.

We encourage using this rather than calling print directly.

Returns false. Why? Because diag() is often used in conjunction with a failing test (ok() || diag()) it "passes through" the failure.

return ok(...) || diag(...);

Like diag(), but it prints to the output() handle so it will not normally be seen by the user except in verbose mode.

my @dump = $Test->explain(@msgs);

Will dump the contents of any references in a human readable format. Handy for things like...

is_deeply($have, $want) || diag explain $have;


is_deeply($have, $want) || note explain $have;
my $filehandle = $Test->output;

These methods control where Test::Builder will print its output. They take either an open $filehandle, a $filename to open and write to or a $scalar reference to append to. It will always return a $filehandle.

output is where normal "ok/not ok" test output goes.

Defaults to STDOUT.

failure_output is where diagnostic output on test failures and diag() goes. It is normally not read by Test::Harness and instead is displayed to the user.

Defaults to STDERR.

todo_output is used instead of failure_output() for the diagnostics of a failing TODO test. These will not be seen by the user.

Defaults to STDOUT.


Resets all the output filehandles back to their defaults.


Warns with @message but the message will appear to come from the point where the original test function was called ($tb->caller).


Dies with @message but the message will appear to come from the point where the original test function was called ($tb->caller).

Test Status and Info

my $curr_test = $Test->current_test;

Gets/sets the current test number we're on. You usually shouldn't have to set this.

If set forward, the details of the missing tests are filled in as 'unknown'. if set backward, the details of the intervening tests are deleted. You can erase history if you really want to.

my $ok = $builder->is_passing;

Indicates if the test suite is currently passing.

More formally, it will be false if anything has happened which makes it impossible for the test suite to pass. True otherwise.

For example, if no tests have run is_passing() will be true because even though a suite with no tests is a failure you can add a passing test to it and start passing.

Don't think about it too much.

my @tests = $Test->summary;

A simple summary of the tests so far. True for pass, false for fail. This is a logical pass/fail, so todos are passes.

Of course, test #1 is $tests[0], etc...

my @tests = $Test->details;

Like summary(), but with a lot more detail.

$tests[$test_num - 1] = 
        { 'ok'       => is the test considered a pass?
          actual_ok  => did it literally say 'ok'?
          name       => name of the test (if any)
          type       => type of test (if any, see below).
          reason     => reason for the above (if any)

'ok' is true if Test::Harness will consider the test to be a pass.

'actual_ok' is a reflection of whether or not the test literally printed 'ok' or 'not ok'. This is for examining the result of 'todo' tests.

'name' is the name of the test.

'type' indicates if it was a special test. Normal tests have a type of ''. Type can be one of the following:

skip        see skip()
todo        see todo()
todo_skip   see todo_skip()
unknown     see below

Sometimes the Test::Builder test counter is incremented without it printing any test output, for example, when current_test() is changed. In these cases, Test::Builder doesn't know the result of the test, so its type is 'unknown'. These details for these tests are filled in. They are considered ok, but the name and actual_ok is left undef.

For example "not ok 23 - hole count # TODO insufficient donuts" would result in this structure:

$tests[22] =    # 23 - 1, since arrays start from 0.
  { ok        => 1,   # logically, the test passed since its todo
    actual_ok => 0,   # in absolute terms, it failed
    name      => 'hole count',
    type      => 'todo',
    reason    => 'insufficient donuts'
my $todo_reason = $Test->todo;
my $todo_reason = $Test->todo($pack);

If the current tests are considered "TODO" it will return the reason, if any. This reason can come from a $TODO variable or the last call to todo_start().

Since a TODO test does not need a reason, this function can return an empty string even when inside a TODO block. Use $Test->in_todo to determine if you are currently inside a TODO block.

todo() is about finding the right package to look for $TODO in. It's pretty good at guessing the right package to look at. It first looks for the caller based on $Level + 1, since todo() is usually called inside a test function. As a last resort it will use exported_to().

Sometimes there is some confusion about where todo() should be looking for the $TODO variable. If you want to be sure, tell it explicitly what $pack to use.

my $todo_reason = $Test->find_TODO();
my $todo_reason = $Test->find_TODO($pack);

Like todo() but only returns the value of $TODO ignoring todo_start().

Can also be used to set $TODO to a new value while returning the old value:

my $old_reason = $Test->find_TODO($pack, 1, $new_reason);
my $in_todo = $Test->in_todo;

Returns true if the test is currently inside a TODO block.


This method allows you declare all subsequent tests as TODO tests, up until the todo_end method has been called.

The TODO: and $TODO syntax is generally pretty good about figuring out whether or not we're in a TODO test. However, often we find that this is not possible to determine (such as when we want to use $TODO but the tests are being executed in other packages which can't be inferred beforehand).

Note that you can use this to nest "todo" tests

$Test->todo_start('working on this');
# lots of code
$Test->todo_start('working on that');
# more code

This is generally not recommended, but large testing systems often have weird internal needs.

We've tried to make this also work with the TODO: syntax, but it's not guaranteed and its use is also discouraged:

    local $TODO = 'We have work to do!';
    $Test->todo_start('working on this');
    # lots of code
    $Test->todo_start('working on that');
    # more code

Pick one style or another of "TODO" to be on the safe side.


Stops running tests as "TODO" tests. This method is fatal if called without a preceding todo_start method call.

my $package = $Test->caller;
my($pack, $file, $line) = $Test->caller;
my($pack, $file, $line) = $Test->caller($height);

Like the normal caller(), except it reports according to your level().

$height will be added to the level().

If caller() winds up off the top of the stack it report the highest context.


If all your tests passed, Test::Builder will exit with zero (which is normal). If anything failed it will exit with how many failed. If you run less (or more) tests than you planned, the missing (or extras) will be considered failures. If no tests were ever run Test::Builder will throw a warning and exit with 255. If the test died, even after having successfully completed all its tests, it will still be considered a failure and will exit with 255.

So the exit codes are...

0                   all tests successful
255                 test died or all passed but wrong # of tests run
any other number    how many failed (including missing or extras)

If you fail more than 254 tests, it will be reported as 254.


In perl 5.8.1 and later, Test::Builder is thread-safe. The test number is shared amongst all threads. This means if one thread sets the test number using current_test() they will all be effected.

While versions earlier than 5.8.1 had threads they contain too many bugs to support.

Test::Builder is only thread-aware if is loaded before Test::Builder.


An informative hash, accessible via <details()>, is stored for each test you perform. So memory usage will scale linearly with each test run. Although this is not a problem for most test suites, it can become an issue if you do large (hundred thousands to million) combinatorics tests in the same run.

In such cases, you are advised to either split the test file into smaller ones, or use a reverse approach, doing "normal" (code) compares and triggering fail() should anything go unexpected.

Future versions of Test::Builder will have a way to turn history off.


CPAN can provide the best examples. Test::Simple, Test::More, Test::Exception and Test::Differences all use Test::Builder.


Test::Simple, Test::More, Test::Harness


Original code by chromatic, maintained by Michael G Schwern <>


Copyright 2002-2008 by chromatic <> and Michael G Schwern <>.

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