Updated the test system

test/formatDuration.test.js

@@ -0,0 +1,14 @@
+const expect = require('expect');
+const {formatDuration} = require('./_30s.js');
+
+test('formatDuration is a Function', () => {
+  expect(formatDuration).toBeInstanceOf(Function);
+});
+test('Returns the human readable format of the given number of milliseconds', () => {
+  expect(formatDuration(1001)).toBe('1 second, 1 millisecond');
+});
+test('Returns the human readable format of the given number of milliseconds', () => {
+  expect(formatDuration(34325055574)).toBe(
+    '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'
+  );
+});