Updated the test system

test/isPromiseLike.test.js

@@ -0,0 +1,18 @@
+const expect = require('expect');
+const {isPromiseLike} = require('./_30s.js');
+
+test('isPromiseLike is a Function', () => {
+  expect(isPromiseLike).toBeInstanceOf(Function);
+});
+test('Returns true for a promise-like object', () => {
+  expect(
+    isPromiseLike({
+      then: function() {
+        return '';
+      }
+    })
+  ).toBeTruthy();
+});
+test('Returns false for an empty object', () => {
+  expect(isPromiseLike({})).toBeFalsy();
+});