spy on a method

MethodSpy.js

		function MethodSpy (method, context) {
			var count, orig, spy;

			count = 0;
			orig = context[method];
			
			context[method] = function () {
				count++;
				return orig.apply(context, arguments);
			};

			return {
				calledNever: function () { return count == 0; },
				calledOnce: function () { return count == 1; },
				calledTwice: function () { return count == 2; },
				calledMany: function (howMany) { return count == howMany; },
				unspy: function () { context[method] = orig; }
			};
		}