PHP - 致命错误:调用未定义的函数test()

I'm stuck on this register form. I have an error with this code:

Fatal error: Call to undefined function test() in C:\wamp\www daiegister.php on line 21

I can't figure it out what the error is or where i can fix it.

Php:

include('db.php');

$message = '';
$x = '';
$t='';
$num1 = '';
$num2 = '';
$num3 = '';


if(isset($_POST['submit'])){
    //pra randum number
    $adminNo = $num1 . $num2 . $num3; 

    $name = trim($_POST['name']);
    $username = trim($_POST['username']);
    $password = trim($_POST['password']);
    $function = "admin";

    $list = test($username);
    foreach($list as $t){
        $x = $t['userName'];
    }

    if(strlen($username) < 6){ //IF THE USERNAME LENGTH IS LESSER THAN 5
        $message = 'Username must be greater than 5 characters.';
    } else if($username === $x){ //IF THE USERNAME IS ALREADY TAKEN
            $message = 'Username is already taken.';
    } else {
        $message = register($adminNo, $username, $password, $fullname, $function);
        echo"<script>alert('Successfully registered!');
                window.location='login.php'
            </script>";
    }

}

Html:

<body>  
  <form method = "post">
    <input type="text" placeholder="fullname" name="name" /><br>
    <input type="text" placeholder="username" name="username" /><br>
    <input type="password" placeholder="password" name="password" /><br>
    <input type="submit" name="submit"  value="register" />
    <?php echo $message;?>
  </form>
</body>

you may want to include or require the file that has this function or add it to the top, before the if statement

function test() {}
function register() {}

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The problem with your code is exactly what the error says; you're calling an undefined function named test().

You try to define a variable $list and give it the value test($username). What you are doing here is passing $username to the test() method.

According to your code $username should contain something passed through the POST global variable but you didn't actually define test() anywhere.

I'm not sure what you're trying to accomplish seeing as a function named "test" could be doing anythning.

Either remove the line $list = test($username); from your code or define test()

There is no $fullname..

$message = register($adminNo, $username, $password, $name, $function);

No description of test().