Updated the test system

test/pick.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {pick} = require('./_30s.js');
+
+test('pick is a Function', () => {
+  expect(pick).toBeInstanceOf(Function);
+});
+test('Picks the key-value pairs corresponding to the given keys from an object.', () => {
+  expect(pick({ a: 1, b: '2', c: 3 }, ['a', 'c'])).toEqual({ a: 1, c: 3 });
+});