(PHP 4 >= 4.0.2, PHP 5)
mcrypt_module_self_test — This function runs a self test on the specified module
$algorithm
   [, string $lib_dir
  ] )This function runs the self test on the algorithm specified.
algorithmOne of the MCRYPT_ciphername constants, or the name of the algorithm as string.
lib_dir
       The optional lib_dir parameter can contain the
       location where the algorithm module is on the system.
      
   The function returns TRUE if the self test succeeds, or FALSE when it
   fails.
  
Example #1 mcrypt_module_self_test() example
<?php
var_dump(mcrypt_module_self_test(MCRYPT_RIJNDAEL_128)) . "\n";
var_dump(mcrypt_module_self_test(MCRYPT_BOGUS_CYPHER));
?>
The above example will output:
bool(true) bool(false)