Testing/mocking stdlib function

gistfile1.txt

<?php
/*
This is a contrived example - but I'm working on a large PHPv4 style legacy codebase 
and it's full of this kind of code (only much, much worse - c70,000 lines of raw
mysql calls etc).  

So in this case I could use the 'namespace' mocking trick to mock all of the 
functions - but to test things like "everything passes", "connection works, but TLS 
fails", "password is wrong" etc, seems hard to do without the tests 
getting really quite nasty.  Combined with all the raw mysql* function calls it
makes writing tests/refactoring much more, ahem, 'exciting' than I'd like ;-)
*/

function auth_ldap($username, $password, $server, $ou)
{
  $ldapconn = ldap_connect($server);
  if (!$ldapconn) {
    return "Could not connect to server!";
  }

  if (! ldap_start_tls($ldapconn)) {
    return "Could not start TLS connection to server!";
  }

  $ldapbind = @ldap_bind($ldapconn);
  $search = ldap_search($ldapconn, $ou, "uid={$username}");
  if (ldap_count_entries($ldapconn, $search) != 1) {
    ldap_unbind($ldapconn);
    return "Could not find user!";
  }
  $info = ldap_get_entries($ldapconn, $search);
  $ldapbind = @ldap_bind($ldapconn, $info[0]['dn'], $password);
  if (!$ldapbind) {
    ldap_unbind($ldapconn);
    return "Could not authenticate user!";
  }
  $search = ldap_search($ldapconn, $ou, "uid={$username}");
  $info = ldap_get_entries($ldapconn, $search);
  $userData = array(
    'username' => $username,
    'surname' => $info[0]['sn'][0],
    'forenames' => $info[0]['givenname'][0],
    'email' => $info[0]['mail'][0],
  );
  ldap_unbind($ldapconn);
  return $userData;
}