Updated the test system

test/isNil.test.js

@@ -0,0 +1,15 @@
+const expect = require('expect');
+const {isNil} = require('./_30s.js');
+
+test('isNil is a Function', () => {
+  expect(isNil).toBeInstanceOf(Function);
+});
+test('Returns true for null', () => {
+  expect(isNil(null)).toBeTruthy();
+});
+test('Returns true for undefined', () => {
+  expect(isNil(undefined)).toBeTruthy();
+});
+test('Returns false for an empty string', () => {
+  expect(isNil('')).toBeFalsy();
+});