// Sinon spy function
var callback = sinon.spy();
callback();
callback.called;
callback.callCount;
callback.calledWith(arg1);
callback.threw();
callback.returned(obj);
callback.calledBefore(spy);
callback.calledAfter(spy);

// Sinon spy method
sinon.spy($, "ajax");
$.ajax({ / ... / });
var call = $.ajax.getCall(0);
call.args;
call.exception;
call.returnValue;
$.ajax.restore();