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Test::Harness - run perl standard test scripts with statistics


use Test::Harness;



STOP! If all you want to do is write a test script, consider using Test::Simple. Otherwise, read on.

(By using the Test module, you can write test scripts without knowing the exact output this module expects. However, if you need to know the specifics, read on!)

Perl test scripts print to standard output "ok N" for each single test, where N is an increasing sequence of integers. The first line output by a standard test script is "1..M" with M being the number of tests that should be run within the test script. Test::Harness::runtests(@tests) runs all the testscripts named as arguments and checks standard output for the expected "ok N" strings.

After all tests have been performed, runtests() prints some performance statistics that are computed by the Benchmark module.

The test script output

The following explains how Test::Harness interprets the output of your test program.


This header tells how many tests there will be. For example, 1..10 means you plan on running 10 tests. This is a safeguard in case your test dies quietly in the middle of its run.

It should be the first non-comment line output by your test program.

In certain instances, you may not know how many tests you will ultimately be running. In this case, it is permitted for the 1..M header to appear as the last line output by your test (again, it can be followed by further comments).

Under no circumstances should 1..M appear in the middle of your output or more than once.

'ok', 'not ok'. Ok?

Any output from the testscript to standard error is ignored and bypassed, thus will be seen by the user. Lines written to standard output containing /^(not\s+)?ok\b/ are interpreted as feedback for runtests(). All other lines are discarded.

/^not ok/ indicates a failed test. /^ok/ is a successful test.

test numbers

Perl normally expects the 'ok' or 'not ok' to be followed by a test number. It is tolerated if the test numbers after 'ok' are omitted. In this case Test::Harness maintains temporarily its own counter until the script supplies test numbers again. So the following test script

print <<END;
not ok
not ok

will generate

FAILED tests 1, 3, 6
Failed 3/6 tests, 50.00% okay
test names

Anything after the test number but before the # is considered to be the name of the test.

ok 42 this is the name of the test

Currently, Test::Harness does nothing with this information.

Skipping tests

If the standard output line contains the substring # Skip (with variations in spacing and case) after ok or ok NUMBER, it is counted as a skipped test. If the whole testscript succeeds, the count of skipped tests is included in the generated output. Test::Harness reports the text after # Skip\S*\s+ as a reason for skipping.

ok 23 # skip Insufficient flogiston pressure.

Similarly, one can include a similar explanation in a 1..0 line emitted if the test script is skipped completely:

1..0 # Skipped: no leverage found
Todo tests

If the standard output line contains the substring # TODO after not ok or not ok NUMBER, it is counted as a todo test. The text afterwards is the thing that has to be done before this test will succeed.

not ok 13 # TODO harness the power of the atom

These tests represent a feature to be implemented or a bug to be fixed and act as something of an executable "thing to do" list. They are not expected to succeed. Should a todo test begin succeeding, Test::Harness will report it as a bonus. This indicates that whatever you were supposed to do has been done and you should promote this to a normal test.

Bail out!

As an emergency measure, a test script can decide that further tests are useless (e.g. missing dependencies) and testing should stop immediately. In that case the test script prints the magic words

Bail out!

to standard output. Any message after these words will be displayed by Test::Harness as the reason why testing is stopped.


Additional comments may be put into the testing output on their own lines. Comment lines should begin with a '#', Test::Harness will ignore them.

ok 1
# Life is good, the sun is shining, RAM is cheap.
not ok 2
# got 'Bush' expected 'Gore'
Anything else

Any other output Test::Harness sees it will silently ignore BUT WE PLAN TO CHANGE THIS! If you wish to place additional output in your test script, please use a comment.

Taint mode

Test::Harness will honor the -T in the #! line on your test files. So if you begin a test with:

#!perl -T

the test will be run with taint mode on.

Configuration variables.

These variables can be used to configure the behavior of Test::Harness. They are exported on request.


The global variable $Test::Harness::verbose is exportable and can be used to let runtests() display the standard output of the script without altering the behavior otherwise.


The global variable $Test::Harness::switches is exportable and can be used to set perl command line options used for running the test script(s). The default value is -w.


It will happen, your tests will fail. After you mop up your ego, you can begin examining the summary report:

        Test returned status 3 (wstat 768, 0x300)
DIED. FAILED tests 1, 3, 5, 7, 9, 11, 13, 15, 17, 19
        Failed 10/20 tests, 50.00% okay
Failed Test  Stat Wstat Total Fail  Failed  List of Failed
t/waterloo.t    3   768    20   10  50.00%  1 3 5 7 9 11 13 15 17 19
Failed 1/5 test scripts, 80.00% okay. 10/44 subtests failed, 77.27% okay.

Everything passed but t/waterloo.t. It failed 10 of 20 tests and exited with non-zero status indicating something dubious happened.

The columns in the summary report mean:

Failed Test

The test file which failed.


If the test exited with non-zero, this is its exit status.


The wait status of the test umm, I need a better explanation here.


Total number of tests expected to run.


Number which failed, either from "not ok" or because they never ran.


Percentage of the total tests which failed.

List of Failed

A list of the tests which failed. Successive failures may be abbreviated (ie. 15-20 to indicate that tests 15, 16, 17, 18, 19 and 20 failed).


Test::Harness currently only has one function, here it is.

my $allok = runtests(@test_files);

This runs all the given @test_files and divines whether they passed or failed based on their output to STDOUT (details above). It prints out each individual test which failed along with a summary report and a how long it all took.

It returns true if everything was ok. Otherwise it will die() with one of the messages in the DIAGNOSTICS section.

This is just _run_all_tests() plus _show_results()


&runtests is exported by Test::Harness by default.

$verbose and $switches are exported upon request.


All tests successful.\nFiles=%d, Tests=%d, %s

If all tests are successful some statistics about the performance are printed.

FAILED tests %s\n\tFailed %d/%d tests, %.2f%% okay.

For any single script that has failing subtests statistics like the above are printed.

Test returned status %d (wstat %d)

Scripts that return a non-zero exit status, both $? >> 8 and $? are printed in a message similar to the above.

Failed 1 test, %.2f%% okay. %s
Failed %d/%d tests, %.2f%% okay. %s

If not all tests were successful, the script dies with one of the above messages.

FAILED--Further testing stopped: %s

If a single subtest decides that further testing will not make sense, the script dies with this message.



Harness sets this before executing the individual tests. This allows the tests to determine if they are being executed through the harness or by any other means.


This value will be used for the width of the terminal. If it is not set then it will default to COLUMNS. If this is not set, it will default to 80. Note that users of Bourne-sh based shells will need to export COLUMNS for this module to use that variable.


When true it will make harness attempt to compile the test using perlcc before running it.

NOTE This currently only works when sitting in the perl source directory!


When set to the name of a directory, harness will check after each test whether new files appeared in that directory, and report them as

LEAKED FILES: scr.tmp 0 my.db

If relative, directory name is with respect to the current directory at the moment runtests() was called. Putting absolute path into HARNESS_FILELEAK_IN_DIR may give more predictable results.


Makes harness ignore the exit status of child processes when defined.


When set to a true value, forces it to behave as though STDOUT were not a console. You may need to set this if you don't want harness to output more frequent progress messages using carriage returns. Some consoles may not handle carriage returns properly (which results in a somewhat messy output).


If true, the ok messages are printed out only every second. This reduces output and therefore may for example help testing over slow connections.


Its value will be prepended to the switches used to invoke perl on each test. For example, setting HARNESS_PERL_SWITCHES to -W will run all tests with all warnings enabled.


If true, Test::Harness will output the verbose results of running its tests. Setting $Test::Harness::verbose will override this.


Here's how Test::Harness tests itself

$ cd ~/src/devel/Test-Harness
$ perl -Mblib -e 'use Test::Harness qw(&runtests $verbose);
  $verbose=0; runtests @ARGV;' t/*.t
Using /home/schwern/src/devel/Test-Harness/blib
All tests successful.
Files=4, Tests=24, 2 wallclock secs ( 0.61 cusr + 0.41 csys = 1.02 CPU)


Test and Test::Simple for writing test scripts, Benchmark for the underlying timing routines, Devel::CoreStack to generate core dumps from failed tests and Devel::Cover for test coverage analysis.


Either Tim Bunce or Andreas Koenig, we don't know. What we know for sure is, that it was inspired by Larry Wall's TEST script that came with perl distributions for ages. Numerous anonymous contributors exist. Andreas Koenig held the torch for many years, and then Michael G Schwern.

Current maintainer is Andy Lester <>.


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



Provide a way of running tests quietly (ie. no printing) for automated validation of tests. This will probably take the form of a version of runtests() which rather than printing its output returns raw data on the state of the tests. (Partially done in Test::Harness::Straps)

Document the format.

Fix HARNESS_COMPILE_TEST without breaking its core usage.

Figure a way to report test names in the failure summary.

Rework the test summary so long test names are not truncated as badly. (Partially done with new skip test styles)

Deal with VMS's "not \nok 4\n" mistake.

Add option for coverage analysis.


Implement Straps total_results()

Remember exit code

Completely redo the print summary code.

Implement Straps callbacks. (experimentally implemented)

Straps->analyze_file() not taint clean, don't know if it can be

Fix that damned VMS nit.

HARNESS_TODOFAIL to display TODO failures

Add a test for verbose.

Change internal list of test results to a hash.

Fix stats display when there's an overrun.

Fix so perls with spaces in the filename work.

Keeping whittling away at _run_all_tests()

Clean up how the summary is printed. Get rid of those damned formats.


HARNESS_COMPILE_TEST currently assumes it's run from the Perl source directory.