Updated the test system

test/size.test.js

@@ -0,0 +1,12 @@
+const expect = require('expect');
+const {size} = require('./_30s.js');
+
+test('size is a Function', () => {
+  expect(size).toBeInstanceOf(Function);
+});
+test('Get size of arrays, objects or strings.', () => {
+  expect(size([1, 2, 3, 4, 5])).toBe(5);
+});
+test('Get size of arrays, objects or strings.', () => {
+  expect(size({ one: 1, two: 2, three: 3 })).toBe(3);
+});