Hi so i am trying to make a login system using mysql and php but i constantly get the error

Warning: mysql_connect(): Access denied for user 'testuser'@'localhost' (using password: YES) in E:\PHP_Runner\php\root\process.php on line 10

The user is created as seen in the Any suggestions/help?

<?php
$username = $_POST['user'];
$password = $_POST['pass'];

$username = stripcslashes($username);
$password = stripcslashes($password);
$username = mysql_real_escape_string($username);
$password = mysql_real_escape_string($password);

mysql_connect("localhost",$username, $password) or die("Could not connect to database");
mysql_select_db("users");

$result = mysql_query("select * from users where username = '$username' and password = '$password'")
        or die("Failed to query database" .mysql_error());

$row = mysql_fetch_array($result);
if($row['username'] == $username && $row['password'] == $password){
echo "Login success !! welcome".$row['username'];
}else{
    echo "Failed to login";
}

?>