use Test::More 'no_plan';

my $escaped = 'st\x{f9}';
my $bytes   = "st\x{f9}";

ok( $escaped ne $bytes, '$escaped ne $bytes' );

my $unescaped = $escaped;
$unescaped =~ s{ \\x\{ ([a-f0-9]{2}) \} }{ chr hex $1 }xmseg;

is( $unescaped, $bytes, '$unescaped eq $bytes' );