Updated the test system

test/isUndefined.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {isUndefined} = require('./_30s.js');
+
+test('isUndefined is a Function', () => {
+  expect(isUndefined).toBeInstanceOf(Function);
+});
+test('Returns true for undefined', () => {
+  expect(isUndefined(undefined)).toBeTruthy();
+});