Updated the test system

test/isNumber.test.js

@@ -0,0 +1,12 @@
+const expect = require('expect');
+const {isNumber} = require('./_30s.js');
+
+test('isNumber is a Function', () => {
+  expect(isNumber).toBeInstanceOf(Function);
+});
+test('passed argument is a number', () => {
+  expect(isNumber(1)).toBeTruthy();
+});
+test('passed argument is not a number', () => {
+  expect(isNumber('1')).toBeFalsy();
+});