Test::Harness - Run Perl standard test scripts with statistics


Version 2.56


  use Test::Harness;


STOP! If all you want to do is write a test script, consider using Test::Simple. Test::Harness is the module that reads the output from Test::Simple, Test::More and other modules based on Test::Builder. You don't need to know about Test::Harness to use those modules.

Test::Harness runs tests and expects output from the test in a certain format. That format is called TAP, the Test Anything Protocol. It is defined in the Test::Harness::TAP manpage.

Test::Harness::runtests(@tests) runs all the testscripts named as arguments and checks standard output for the expected strings in TAP format.

The prove utility is a thin wrapper around Test::Harness.

Taint mode

Test::Harness will honor the -T or -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 package 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 prove utility's -v flag will set this.


The package 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 overrides HARNESS_SWITCHES.


If set to true, and Time::HiRes is available, print elapsed seconds after each test file.


When tests fail, analyze 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.


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.


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

$verbose, $switches and $debug 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.


Test::Harness sets these before executing the individual tests.


This is set to a true value. It allows the tests to determine if they are being executed through the harness or by any other means.


This is the version of Test::Harness.



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!


If true, Test::Harness will print debugging information about itself as it runs the tests. This is different from HARNESS_VERBOSE, which prints the output from the test being run. Setting $Test::Harness::Debug will override this, or you can use the -d switch in the prove utility.


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).


Usually your tests will be run by $^X, the currently-executing Perl. However, you may want to have it run by a different executable, such as a threading perl, or a different version.

If you're using the prove utility, you can use the --perl switch.


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, or you can use the -v switch in the prove utility.


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)


The included prove utility for running test scripts from the command line, the Test manpage and the Test::Simple manpage for writing test scripts, the Benchmark manpage for the underlying timing routines, and the Devel::Cover manpage for test coverage analysis.


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)

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.

Please use the CPAN bug ticketing system at You can also mail bugs, fixes and enhancements to <bug-test-harness at>.


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 <andy at>.


Copyright 2002-2005 by Michael G Schwern <schwern at>, Andy Lester <andy at>.

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