Updated the test system

test/isFunction.test.js

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