diff --git a/lab2/main_test.js b/lab2/main_test.js
index 5034468e..e11f63be 100644
--- a/lab2/main_test.js
+++ b/lab2/main_test.js
@@ -1,6 +1,91 @@
 const test = require('node:test');
+const fs = require('fs');
 const assert = require('assert');
 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
+
+// create name_list.txt for testing
+fs.writeFileSync('name_list.txt', 'John\nJane');
+
+test('MailSystem write function', () => {
+    const mailSystem = new MailSystem();
+    assert.strictEqual(mailSystem.write('John'), 'Congrats, John!');
+    assert.strictEqual(mailSystem.write(123), 'Congrats, 123!');
+    assert.strictEqual(mailSystem.write(''), 'Congrats, !');
+    assert.strictEqual(mailSystem.write(), 'Congrats, undefined!');
+    assert.strictEqual(mailSystem.write(null), 'Congrats, null!');
+    assert.strictEqual(mailSystem.write(true), 'Congrats, true!');
+});
+
+test('MailSystem send function', (t) => {
+    // mock Math.random to control the return value
+    const mailSystem = new MailSystem();
+    const mock_random = t.mock.method(Math, 'random');
+    mock_random.mock.mockImplementation(() => 0.6);
+    assert.strictEqual(mailSystem.send('John', 'Congrats, John!'), true);
+    mock_random.mock.mockImplementation(() => 0.4);
+    assert.strictEqual(mailSystem.send('John', 'Congrats, John!'), false);
+});
+
+
+test('Application constructor', () => {
+    const application = new Application();
+    assert.strictEqual(application.people.length, 0);
+    assert.strictEqual(application.selected.length, 0);
+    assert.strictEqual(application.mailSystem instanceof MailSystem, true);
+    assert.strictEqual(application.getNames() instanceof Promise, true);
+});
+
+test('Application getNames function', async () => {
+    const application = new Application();
+    const [people, select] = await application.getNames();
+    assert.deepStrictEqual(people, ['John', 'Jane']);
+    assert.deepStrictEqual(select, []);
+});
+
+test('Application getRandomPerson function', async (t) => {
+    // mock Math.floor to control the return value
+    const mock_floor = t.mock.method(Math, 'floor');
+    const application = new Application();
+    await application.getNames();
+    mock_floor.mock.mockImplementation(() => 0);
+    assert.strictEqual(application.getRandomPerson(), 'John');
+    mock_floor.mock.mockImplementation(() => 1);
+    assert.strictEqual(application.getRandomPerson(), 'Jane');
+    mock_floor.mock.mockImplementation(() => 2);
+    assert.strictEqual(application.getRandomPerson(), undefined);
+});
+
+test('Application selectNextPerson function', async (t) => {
+    // mock getRandomPerson to control the return value
+    const application = new Application();
+    application.count = 0;
+    const mock_getRandomPerson = t.mock.method(application, 'getRandomPerson');
+    mock_getRandomPerson.mock.mockImplementation(() => {
+        if (application.count !== 2) {
+            application.count++;
+            return 'John';
+        } else {
+            return 'Jane';
+        }
+    });
+    await application.getNames();
+    assert.strictEqual(application.selectNextPerson(), 'John');
+    assert.strictEqual(application.selectNextPerson(), 'Jane');
+    assert.strictEqual(application.selectNextPerson(), null);
+});
+
+test('Application notifySelected function', (t) => {
+    // spy on send and write functions
+    const application = new Application();
+    application.selected = ['John', 'Jane'];
+    const spy_send = t.mock.method(application.mailSystem, 'send');
+    const spy_write = t.mock.method(application.mailSystem, 'write');
+    application.notifySelected();
+    assert.strictEqual(spy_send.mock.calls.length, 2);
+    assert.strictEqual(spy_write.mock.calls.length, 2);
+}).then(() => {
+    fs.unlinkSync('name_list.txt');
+});
\ No newline at end of file