[CI2] add_slashes for inserting Data to DB

Hi,

I am using mysqli, and using below query

$test = htmlspecialchars(addslashes($this->input->post('test')));

$sql = "SELECT * from table WHERE file_id = '$test'";
$query = $this->db->query($sql);

I tried sample scripts of SQL injections, and looks it avoids all sql injection codes. 
ex)
INSERT INTO User (name) VALUES (?);
Robert'); DROP TABLE User; 

Is this fine way to use in CI2?

Thank you