well as you can see im trying to test my anti-sql injector

Code:
<FORM METHOD=POST ACTION="Inject.php">
<CENTER><INPUT NAME="IJz" TYPE="text"></CENTER>
<CENTER><INPUT VALUE="Anti-Inject" TYPE="submit"></CENTER>
</FORM>

<?php
if ($_GET['$submit']){
$Test = AntiInject($_POST['IJz']);
echo '$test';
}

//Anti-Injection
function AntiInject($sql){
$sql = str_replace("SELECT", "", $sql);
return $sql;
}
?>
everything seems to go wrong... I type SQL Injection text into the box, press Submit and i want it to echo the results after going through AntiInject(); im just using the word SELECT to see if it works.

any help?