A couple of relevant threads:

• Is there any way to override "file test operator"?
• mocking overloading filetest operator callback -f -d -e -X
• StackOverflow: mocking -d -f and friends. How to put them into CORE::GLOBAL
• Overriding filetest operators via overriding stat()?

And quoting myself from the last of those links: All of this seems to indicate that what you want is unfortunately not directly possible. One possible solution, although not the most satisfying, is to abstract the test out into a function that can be mocked...

sub check_perms {
    my $filename = shift;
    return -f -w -x $filename;
}
check_perms("filename") or die;
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Hello Doctrin,

I haven’t tried it, but here is an excerpt from the documentation for the core overload pragma, under “Overloadable Operations”:

• File tests
  
  The key '-X' is used to specify a subroutine to handle all the filetest operators (-f, -x, and so on: see -X for the full list); it is not possible to overload any filetest operator individually. To distinguish them, the letter following the '-' is passed as the second argument (that is, in the slot that for binary operators is used to pass the second operand).
  
  Calling an overloaded filetest operator does not affect the stat value associated with the special filehandle _. It still refers to the result of the last stat, lstat or unoverloaded filetest.
  
  This overload was introduced in Perl 5.12.

Hope that helps,

Note that this only works if the thing that you're calling the -X on is an object of the overloaded class.

use warnings;
use strict;

{
    package Foo;
    use Data::Dump;
    use overload fallback=>0,
        '-X' => sub { dd @_; return 1 };
}

my $foo = bless {}, 'Foo';
print -e $foo ? 'yes' : 'no', "\n";
my $bar = "doesnotexist";
print -e $bar ? 'yes' : 'no', "\n";

__END__

(bless({}, "Foo"), "e", "")
yes
no
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