Updated the test system

test/randomHexColorCode.test.js

@@ -0,0 +1,19 @@
+const expect = require('expect');
+const {randomHexColorCode} = require('./_30s.js');
+
+test('randomHexColorCode is a Function', () => {
+  expect(randomHexColorCode).toBeInstanceOf(Function);
+});
+test('randomHexColorCode has to proper length', () => {
+  expect(randomHexColorCode().length).toBe(7);
+});
+test('The color code starts with "#"', () => {
+  expect(randomHexColorCode().startsWith('#')).toBeTruthy();
+});
+test('The color code contains only valid hex-digits', () => {
+  expect(
+    randomHexColorCode()
+      .slice(1)
+      .match(/[^0123456789abcdef]/i) === null
+  ).toBeTruthy();
+});