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
Test::Harness::TAP.

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.