Updated the test system

test/pickBy.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {pickBy} = require('./_30s.js');
+
+test('pickBy is a Function', () => {
+  expect(pickBy).toBeInstanceOf(Function);
+});
+test('Creates an object composed of the properties the given function returns truthy for.', () => {
+  expect(pickBy({ a: 1, b: '2', c: 3 }, x => typeof x === 'number')).toEqual({ a: 1, c: 3 });
+});