Updated the test system

test/mapValues.test.js

@@ -0,0 +1,13 @@
+const expect = require('expect');
+const {mapValues} = require('./_30s.js');
+
+test('mapValues is a Function', () => {
+  expect(mapValues).toBeInstanceOf(Function);
+});
+const users = {
+  fred: { user: 'fred', age: 40 },
+  pebbles: { user: 'pebbles', age: 1 }
+};
+test('Maps values', () => {
+  expect(mapValues(users, u => u.age)).toEqual({ fred: 40, pebbles: 1 });
+});