Updated the test system

test/digitize.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {digitize} = require('./_30s.js');
+
+test('digitize is a Function', () => {
+  expect(digitize).toBeInstanceOf(Function);
+});
+test('Converts a number to an array of digits', () => {
+  expect(digitize(123)).toEqual([1, 2, 3]);
+});