Ken Williams' Path-Class module has a test file (t/01-basic.t) that begins with: 
BEGIN {
  $^O = 'Unix'; # Test in Unix mode
}

[download]
Without that override, many tests fail on Windows because paths that are expected to contain '/' are detected as instead containing '\\'.
And there are also cases of an expected empty string being detected as '0'.
Try building Path::Class on Windows and watch it pass - then comment out the BEGIN{} block in t/01-basic.t and examine the failures then elicited by that script.
(BTW, I don't know how that override hack even works.)

The trouble is that, beginning with perl-5.34.0, this hack fails to deliver because running 'perl -Mblib t/01-basic.t' fails in the way already outlined above, irrespective of whether that override is included or commented out.
In addition (with perl-5.34.0 onwards and the BEGIN{} block included), t/01-basic.t fails in an entirely different way when run inside the Test::Harness (as part of 'make test'): 
t/01-basic.t .......... 1/78 Can't call method "relative" on an undefi
+ned value
at C:\sisyphusion\Path-Class-0.37\blib\lib/Path/Class/Entity.pm line 7
+6.
t/01-basic.t .......... Dubious, test returned 22 (wstat 5632, 0x1600)

[download]
What bug(s) should be investigated ?
Is overriding $^O a legitimate thing to do ?
Is it a bug that, on perl-5.34 and later, the "Can't call method "relative"..." error arises ? If so, is it a Path::Class bug ? or a Test::Harness bug ? or a perl bug ?.
Is it a bug that, on perl-5.34 and later, the override loses its effectiveness when run outside Test::Harness ? If so, is it a Path::Class bug ? or a perl bug ?

Cheers,
Rob

In reply to Is it ever legitimate to override $^O ? by syphilis

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