Updated the test system

test/atob.test.js

@@ -0,0 +1,12 @@
+const expect = require('expect');
+const {atob} = require('./_30s.js');
+
+test('atob is a Function', () => {
+  expect(atob).toBeInstanceOf(Function);
+});
+test('atob("Zm9vYmFy") equals "foobar"', () => {
+  expect(atob('Zm9vYmFy')).toBe('foobar');
+});
+test('atob("Z") returns ""', () => {
+  expect(atob('Z')).toBe('');
+});