I thought I had this working earlier today, did something else for a while, then when I came back to it found that the call in the replacement sub is calling itself. The code below demonstrates the problm:

use strict;
use warnings;

use Test::More tests => 1;

my $new;

BEGIN {
    require MIME::Lite;
    $new = MIME::Lite->can ("new");
    undef &MIME::Lite::new;
}

sub MIME::Lite::new {
    print "Validating MIME::Lite::new params\n";
    #goto $new;
    #return $new->(@_);
    return &$new;
}


ok (checkSub (), 'Match existing path');


sub checkSub {
    my $msg = MIME::Lite->new ((To => 'to', ));
    my $result = eval {$msg->send};
}
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For my current tests it's not essential that the original code be called so I can simply return a success value. However that will not always be appropriate. Any idea what I am doing wrong?

None of the "return" variants affect the behaviour.