Updated the test system

test/unescapeHTML.test.js

@@ -0,0 +1,11 @@
+const expect = require('expect');
+const {unescapeHTML} = require('./_30s.js');
+
+test('unescapeHTML is a Function', () => {
+  expect(unescapeHTML).toBeInstanceOf(Function);
+});
+test('Unescapes escaped HTML characters.', () => {
+  expect(unescapeHTML('<a href="#">Me & you</a>')).toBe(
+    '<a href="#">Me & you</a>'
+  );
+});