So siehts ganz gut aus !

node_modules/es5-ext/test/function/is-function.js

@@ -0,0 +1,8 @@
+"use strict";
+
+var o = { call: Function.prototype.call, apply: Function.prototype.apply };
+
+module.exports = function (t, a) {
+	a(t(function () {}), true, "Function is function");
+	a(t(o), false, "Plain object is not function");
+};