Scope Issues With My Javascript Object

I'm having trouble getting the following code to work properly. Every time I try to access the private testing variable from the priveleged MyMethod it gives an error. Says it can't find testing and that it has no properties so I can't run a push() command on it.

function MyClass()
{
var testing = new Array();

// define the method
function MyMethod()
{
this.testing.push("hello");
}

// make the method priveledged
this.MyMethod = MyMethod;
}

// a test function it ensure the variables declared here are isolated
function Start()
{
var myClass = new MyClass();

myClass.MyMethod();

document.write("[" + myClass.testing + "]");
}

Start();