#! perl -slw
use strict;
use constant DIR => '/path/to/dir/';

## temporarially rename the test files 
rename $_, $_ . 'X' for glob DIR . '*.xml';

## And compare the output with a reference file 
## containing the expected output for the no xml case.
system 'perl.exe thescript.pl > noxml.out && diff noxml.out noxml.ref';

## Get the xml files back again.
for my $file ( glob DIR . '*.xmlX' ) {
    my $new = $file;
    chop $new;
    rename $file, $new;
} 

## And test the other three cases by diffing the actual output
## produced by processing 3 test files constructed to demonstrate them
## Against a file containing the expected output.
system 'perl.exe thescript.pl > xml.out && diff xml.out xmp.ref';