Php Form Validation & Security

<?php
    if($_SERVER["REQUEST_METHOD"] == "POST"){

        $fullName = test_input($_POST['fullname']);
        $Email = test_input($_POST['email']);
        $userName = test_input($_POST['username']);
        $passWord = test_input(sha1($_POST['password']));

        echo $fullName . "<br />" . $Email . "<br />" . $userName . "<br />" . $passWord . "<br />";

        if(filter_var($Email,FILTER_VALIDATE_EMAIL)){

            echo 'your email is valid ' . '<br />';

        }else{

            echo 'your email is not valid : try again'  . '<br />';

        }

        if(preg_match('/[\'^£$%&*()}{@#~?><>,|=_+¬-]/',$fullName)){

            echo 'bad full name input ';

        }
        else{

            echo 'good full name input ';
        }
    }

    function test_input($inputField){

        $inputField = htmlspecialchars(stripcslashes(strip_tags($inputField)));
        return $inputField;

    }

?>

<html>
    <head>
        <meta charset='UTF-8'>
        <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
    </head>
<body>

    <form action="<?php htmlspecialchars($_SERVER['PHP_SELF']) ?>" method="POST">
    <h1>CodeJs : Input Validation </h1>

        <div class="form-group">
            <label>Full Name:</label>
            <input type="text" class="form-control" name='fullname'>
        </div>

        <div class="form-group">
            <label>Email address:</label>
            <input type="text" class="form-control" name='email'>
        </div>

        <div class="form-group">
            <label>Username :</label>
            <input type="text" class="form-control" name='username'>
        </div>

        <div class="form-group">
            <label>Password:</label>
            <input type="text" class="form-control" name='password'>
        </div>

        <button type="submit" class="btn btn-default">Submit</button>
    </form>

<style>form{ width: 400px; margin-left: 350px; }</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
</body>
</html>