The "CAVEAT and NOTES" section says:
Test::Harness upgrade
no_plan, todo and done_testing() depend on new Test::Harness
features and fixes. If you're going to distribute tests that use
no_plan or todo your end-users will have to upgrade Test::Harness to
the latest one on CPAN. If you avoid no_plan and TODO tests, the
stock Test::Harness will work fine.
It would be helpful if it said also which version is required, so the
module author could set dependencies in its Makefile.PL/Build.PL/META.yml.