Updated the test system

test/promisify.test.js

@@ -0,0 +1,14 @@
+const expect = require('expect');
+const {promisify} = require('./_30s.js');
+
+test('promisify is a Function', () => {
+  expect(promisify).toBeInstanceOf(Function);
+});
+const x = promisify(Math.max);
+test('Returns a promise', () => {
+  expect(x() instanceof Promise).toBeTruthy();
+});
+test('Runs the function provided', () => {
+  const delay = promisify((d, cb) => setTimeout(cb, d));
+  delay(200).then(() => expect(true).toBeTruthy());
+});