gistfile1.pl

use Test::More;
use Test::Fatal;
use XML::LibXML;

my $escape = sub {
  my $string = shift;
  $string =~ s/&([^;]+(?:\s|<|$))/&amp;$1/g;
  return $string;
};

my $unescaped = "AT&T";
my $escaped = "AT&amp;T";

is($escape->($unescaped), $escaped, "escaped it");
is($escape->($escaped), $escaped, "didn't re-escape it");
is($escape->("<b>$unescaped</b>"), "<b>$escaped</b>", "escaped it with tags");
is($escape->("<b>$escaped</b>"), "<b>$escaped</b>", "didn't re-escape it with tags");

is(
  exception { XML::LibXML->load_xml(string => "<p>".$escape->($unescaped)."</p>") },
  undef,
  "parsed unescaped"
);

is(
  exception { XML::LibXML->load_xml(string => "<p>".$escape->($escaped)."</p>") },
  undef,
  "parsed escaped"
);

like(
  exception { XML::LibXML->load_xml(string => "<p><b>$unescaped</p>") },
  qr/Opening and ending tag mismatch/,
  "error on unclosed tag"
);


done_testing;