the function  arraytolower will create duplicate entries since keys are case sensitive.  

<?php
$array = array('test1' => 'asgAFasDAAd', 'TEST2' => 'ASddhshsDGb', 'TeSt3 '=> 'asdasda@asdadadASDASDgh');

$array = arraytolower($array);
?>
/*
Array
(
    [test1] => asgafasdaad
    [TEST2] => ASddhshsDGb
    [TeSt3] => asdasda@asdadadASDASDgh
    [test2] => asddhshsdgb
    [test3] => asdasda@asdadadasdasdgh
)
*/

I prefer this method

<?php
  function arraytolower($array, $include_leys=false) {
    
    if($include_leys) {
      foreach($array as $key => $value) {
        if(is_array($value))
          $array2[strtolower($key)] = arraytolower($value, $include_leys);
        else
          $array2[strtolower($key)] = strtolower($value);
      }
      $array = $array2;
    }
    else {
      foreach($array as $key => $value) {
        if(is_array($value))
          $array[$key] = arraytolower($value, $include_leys);
        else
          $array[$key] = strtolower($value);   
      }
    }
    
    return $array;
  } 
?>

which when used like this

<?php
$array = $array = array('test1' => 'asgAFasDAAd', 'TEST2' => 'ASddhshsDGb', 'TeSt3 '=> 'asdasda@asdadadASDASDgh');

$array1 = arraytolower($array);
$array2 = arraytolower($array,true);

print_r($array1);
print_r($array2);
?>

will give output of 

Array
(
    [test1] => asgafasdaad
    [TEST2] => asddhshsdgb
    [TeSt3] => asdasda@asdadadasdasdgh
)
Array
(
    [test1] => asgafasdaad
    [test2] => asddhshsdgb
    [test3] => asdasda@asdadadasdasdgh
)