diff --git a/lab2/main_test.js b/lab2/main_test.js
index 5034468e..c10e19a3 100644
--- a/lab2/main_test.js
+++ b/lab2/main_test.js
@@ -1,6 +1,68 @@
 const test = require('node:test');
 const assert = require('assert');
+const fs = require('fs');
+test.mock.method(fs, 'readFile', (file, options, callback) => {
+  callback(null, 'Guan\nChen\nGala');
+});
 const { Application, MailSystem } = require('./main');
 
 // TODO: write your tests here
-// Remember to use Stub, Mock, and Spy when necessary
\ No newline at end of file
+// Remember to use Stub, Mock, and Spy when necessary
+test("Test MailSystem's write", () => {
+    const myClass = new MailSystem()
+    assert.strictEqual( myClass.write("Guan"),"Congrats, Guan!")
+});
+
+test("Test MailSystem's send(name, context)", () => {
+  Math.random = () => 0.6
+    const mailSystem = new MailSystem()
+    const context = mailSystem.write("Guan")
+    const success = mailSystem.send("Guan",context)
+    assert.strictEqual(success,true)
+    Math.random = () => 0.5
+    assert.strictEqual(mailSystem.send("Chen",context),false)
+});
+
+test("Test Application's getNames", async () => {
+  const application = new Application
+  const [people, selected] = await application.getNames()
+  assert.deepStrictEqual(people, ["Guan", "Chen", "Gala"])
+  assert.deepStrictEqual(selected, [])
+});
+
+test("Test Application's getRandomPerson()", (t) => {
+  const application = new Application
+  application.people = ["Guan", "Chen", "Gala"]
+  Math.random = () => 0
+  assert.deepStrictEqual(application.getRandomPerson(), "Guan");
+  Math.random = () => 0.6
+  assert.deepStrictEqual(application.getRandomPerson(), "Chen");
+  Math.random = () => 0.9
+  assert.deepStrictEqual(application.getRandomPerson(), "Gala");
+});
+
+test("Test Application's selectNextPerson",  async() => {
+  const application = new Application
+  const name_list = await application.getNames();
+  application.selected = ["Guan"]
+  let count = 0;
+  test.mock.method(application, 'getRandomPerson', () => {
+      if (count <= name_list.length) { 
+          return name_list[0][count++]; 
+      }
+  });
+  assert.strictEqual(application.selectNextPerson(), "Chen")
+  assert.strictEqual(application.selectNextPerson(), "Gala")
+  assert.strictEqual(application.selectNextPerson(), null)
+});
+
+test("Test Application's notifySelected() ",  () => {
+  const application = new Application  
+  application.people = ["Guan", "Chen", "Gala"]
+  application.selected = ["Guan", "Chen", "Gala"]
+  application.mailSystem.write = test.mock.fn(application.mailSystem.write)
+  application.mailSystem.send = test.mock.fn(application.mailSystem.send)
+  application.notifySelected()
+  assert.strictEqual(application.mailSystem.send.mock.calls.length, application.people.length);
+  assert.strictEqual(application.mailSystem.write.mock.calls.length, application.people.length); 
+});