The second [problem] is how to test any solution on my machine.
in the hope that I will be able to test on my machine
So the situation you need to try to replicate is having a different perl earlier in the path. So on your machine, have a fake directory with an executable file called "perl" that just dies with FAKE PERL or similar. Then put the path to that fake perl earlier in your path than your normal perl. Then run your /path/to/real/prove -l t/ with the full perl path, and when the test suite tries to run the fake perl instead of $^X , it should obviously fail.
edit: as hv pointed out here simultaneous to my post, that is exactly what this post was doing for you: it created a fake perl "executable" (bash script) in your t/ directory, then added that t/ directory to the start of your path; when you run your test suite in that condition, your test script (assuming it still runs perl BLAH rather than $^X BLAH ) would fail.