public function test_a()
 {
     $chars = array('\'' => '&#x27;', '"' => '&quot;', '<' => '&lt;', '>' => '&gt;', '&' => '&amp;', 'Ā' => '&#x0100;', ',' => ',', '.' => '.', '-' => '-', '_' => '_', 'a' => 'a', 'A' => 'A', 'z' => 'z', 'Z' => 'Z', '0' => '0', '9' => '9', "\r" => '&#x0D;', "\n" => '&#x0A;', "\t" => '&#x09;', "" => '&#xFFFD;', '<' => '&lt;', '>' => '&gt;', '&' => '&amp;', '"' => '&quot;', ' ' => '&#x20;');
     foreach ($chars as $key => $val) {
         $this->assertEquals($val, Escaper::a($key), 'Failed to escape: ' . $key);
     }
 }