JQuery :: Plugin - Function (Prototype) Test Unknown

I want to write a plugin, say 'myPlugin' which I can use like
Code:
$('#myID').myPlugin() ;
$('#myID').myPlugin.test() ;

The plugin I wrote looks like
Code:
(function($){
$.fn.myPlugin = function() {
// do something
} $.fn.myPlugin.test = function() {
var $this = $(this) ;
// do something ;
}})(jQuery) ;

This works and it doesn't work. It works because test() is called, but this is not the element with id '#myID' it is $.fn.myPlugin. To fix this I tried the following
Code:
(function($){
$.fn.myPlugin = function() {
// do something
} $.fn.myPlugin.prototype.test = function() {
var $this = $(this) ;
// do something ;
}})(jQuery) ;
but now the function 'test' is unknown.