User role add or remove

This function add role to user if role doesn’t exist.
This function works with plugin multiple-roles.

$user = get_userdata( $user_id );
$roles =  (array) $user->roles; 
if ( !(in_array( 'pending',$roles ) ) ) { 
	$user->add_role( 'pending' );
	$user->remove_role( 'trial_student' );
}