Updated the test system

test/defaults.test.js

@@ -0,0 +1,9 @@
+const expect = require('expect');
+const {defaults} = require('./_30s.js');
+
+test('defaults is a Function', () => {
+  expect(defaults).toBeInstanceOf(Function);
+});
+test('Assigns default values for undefined properties', () => {
+  expect(defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 })).toEqual({ a: 1, b: 2 });
+});