Add MicroTaskScheduler unit tests

Author: gfeun

demo/src/task-scheduler.spec.ts

@@ -0,0 +1,52 @@
+/**
+ * @jest-environment jsdom
+ */
+/// <reference lib="dom" />
+
+import { MicroTaskScheduler } from './task-scheduler';
+
+describe('task-scheduler', () => {
+  let taskScheduler: MicroTaskScheduler;
+  let task: jest.Mock;
+
+  beforeEach(() => {
+    taskScheduler = new MicroTaskScheduler();
+    task = jest.fn();
+  });
+
+  it('should execute task', async () => {
+    taskScheduler.start();
+    taskScheduler.postTask(task);
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    expect(task).toHaveBeenCalledTimes(1);
+  });
+
+  it('should execute task twice when posted twice', async () => {
+    taskScheduler.start();
+    taskScheduler.postTask(task);
+    taskScheduler.postTask(task);
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    expect(task).toHaveBeenCalledTimes(2);
+  });
+
+  it('should not execute task when not started', async () => {
+    taskScheduler.postTask(task);
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    expect(task).not.toHaveBeenCalled();
+  });
+
+  it('should not execute task when stopped', async () => {
+    taskScheduler.start();
+    taskScheduler.stop();
+    taskScheduler.postTask(task);
+    await new Promise((resolve) => setTimeout(resolve, 0));
+    expect(task).not.toHaveBeenCalled();
+  });
+
+  it('should not register listener twice', async () => {
+    const addEventListenerSpy = jest.spyOn(window, 'addEventListener');
+    taskScheduler.start();
+    taskScheduler.start();
+    expect(addEventListenerSpy).toHaveBeenCalledTimes(1);
+  });
+});

demo/src/task-scheduler.ts

@@ -28,7 +28,7 @@ export class MicroTaskScheduler {
   }
 
   private handleMessage = (event: MessageEvent) => {
-    if (event.source === window && event.data === this.messageName) {
+    if (event.data === this.messageName) {
       event.stopPropagation();
       const executeJob = this.executionQueue.shift();
       if (executeJob !== undefined) {