Comment (by Roland Haas):

It requires some Perl POSIX functionality (all in the core language though), namely POSIX fork, pipeand wait. Those exists on all POSIX systems, which is almost all systems Cactus supports (except Windows when used natively ie not via WSL). If these are missing then at worst this simply renders the functionality non-functional but does not prevent regular (serialized) tests from running which does not use fork. Parallel runs may actually work if Perl’s or MSYS / Cygwin’s forkemulation is sufficient, the use statements work fine in MSYS though I have not tested this.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2463/add-option-to-run-tests-in-parallel