Generating test errors with Paypal buttons

[Richard-R]

I have an ASP.NET website that is utilizing the Paypal Buttons.  My Javascript is based upon the sample code I found in the Paypal docs and follows this format:

paypal.Buttons({

   style: {...},

   createOrder: function (data, actions) {...}

   onError: function (err) {...}

   onApprove: function (data, actions) {...}

}).render("#paypal-button-container");

My question is, within the Sandbox environment, how do I go about generating some test error conditions so I can test the onError path of my code?

Thanks,

Richard