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


use Test::Harness;



(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

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 # 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(whatever) as a reason for skipping. Similarly, one can include a similar explanation in a 1..0 line emitted if the test is skipped completely:

1..0 # Skipped: no leverage found


&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.

Setting HARNESS_NOTTY 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).

Setting HARNESS_COMPILE_TEST to a true value will make harness attempt to compile the test using perlcc before running it.

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 value of HARNESS_PERL_SWITCHES 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.

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


Test for writing test scripts and also Benchmark 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.