Updated the test system

test/isEven.test.js

@@ -0,0 +1,12 @@
+const expect = require('expect');
+const {isEven} = require('./_30s.js');
+
+test('isEven is a Function', () => {
+  expect(isEven).toBeInstanceOf(Function);
+});
+test('4 is even number', () => {
+  expect(isEven(4)).toBeTruthy();
+});
+test('5 is not an even number', () => {
+  expect(isEven(5)).toBeFalsy();
+});