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


use Test::Harness;



(By using the the Test manpage 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

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.

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

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.

If the standard output line contains substring <PRE> # Skip </PRE> (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.


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


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.


Setting HARNESS_IGNORE_EXITCODE makes harness ignore the exit status of child processes.

If HARNESS_FILELEAK_IN_DIR is 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 predicatable results.


the Test manpage for writing test scripts and also the Benchmark manpage for the underlying timing routines.


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. Current maintainer is Andreas Koenig.


Test::Harness uses $^X to determine the perl binary to run the tests with. Test scripts running via the shebang (#!) line may not be portable because $^X is not consistent for shebang scripts across platforms. This is no problem when Test::Harness is run with an absolute path to the perl binary or when $^X can be found in the path.


We are painfully aware that these documents may contain incorrect links and misformatted HTML. Such bugs lie in the automatic translation process that automatically created the hundreds and hundreds of separate documents that you find here. Please do not report link or formatting bugs, because we cannot fix per-document problems. The only bug reports that will help us are those that supply working patches to the installhtml or pod2html programs, or to the Pod::HTML module itself, for which I and the entire Perl community will shower you with thanks and praises.

If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.

--Tom Christiansen, Perl Documentation Compiler and Editor

Return to the Perl Documentation Index.
Return to the Perl Home Page.