diff --git a/lab2/main_test.js b/lab2/main_test.js
index 5034468e..4f06d3c6 100644
--- a/lab2/main_test.js
+++ b/lab2/main_test.js
@@ -1,6 +1,147 @@
 const test = require('node:test');
 const assert = require('assert');
+const fs = require('fs');
 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 mailsystem = new MailSystem();
+//     assert.strictEqual(mailsystem.write("John"), 'Congrats, John!');
+// });
+// test("Test MailSystem's send",()=>{
+//     //test('should send mail successfully', () => {
+//         const mailsystem = new MailSystem();
+//         const name = 'John';
+//         Math.random = () => 0.7;
+//         const result = mailsystem.send(name,mailsystem.write(name));
+//         assert.strictEqual(result,true);
+//         Math.random = originalMathRandom;
+
+//         Math.random = () => 0.3;
+//         const result_ = mailsystem.send(name,mailsystem.write(name));
+//         assert.strictEqual(result_,false);
+// });
+
+const data = 'John\nJane\nDoe';
+
+test("Test Application's getNames", async () => {
+    //mock fs.readFile just using test runner
+    fs.writeFileSync('name_list.txt', data, 'utf8');
+    // fs.readFile = (path, encoding, cb) => {
+    //     cb(null, data);
+    // };
+    const app = new Application();
+    const [people,selected] = await app.getNames();
+    assert.deepStrictEqual(people, ['John', 'Jane', 'Doe']);
+    assert.deepStrictEqual(selected, []); 
+    //fs.unlink('name_list.txt', () => {});
+});
+
+
+test("Test Application's getRandomPerson", async () => {
+    let app = new Application();
+    [app.people,app.selected] = await app.getNames();
+    //const originalMathRandom = Math.random;
+        Math.random = () => 0;
+        let result = await app.getRandomPerson();
+        assert.deepStrictEqual(result, 'John');
+        Math.random = () => 0.5;
+        result = await app.getRandomPerson();
+        assert.deepStrictEqual(result, 'Jane');
+        Math.random = () => 0.9;
+        result = await app.getRandomPerson();
+        assert.deepStrictEqual(result, 'Doe');
+        Math.random = originalMathRandom;   
+});
+
+test("Test Application's selectNextPerson", async() => {
+    let app = new Application();
+    [app.people,app.selected] = await app.getNames();
+    //const originalMathRandom = Math.random;
+        //Math.random = () => 0;
+        Math.random = originalMathRandom;
+        Math.random = () => 0;
+        assert.deepStrictEqual(app.selectNextPerson(), 'John');
+        //Math.random = originalMathRandom;
+        Math.random = () => 0.5; 
+        assert.deepStrictEqual(app.selectNextPerson(), 'Jane');
+        //Math.random = () => 0.9;
+        Math.random = originalMathRandom;
+        assert.deepStrictEqual(app.selectNextPerson(), 'Doe');
+        assert.deepStrictEqual(app.selectNextPerson(), null);
+        assert.deepStrictEqual(app.selectNextPerson(), null);
+        assert.deepStrictEqual(app.selectNextPerson(), null);
+        //fs.unlink('name_list.txt', () => {});
+});
+
+test("Test Application's notifySelected", async(t) => {
+    let app = new Application();
+    [app.people,app.selected] = await app.getNames();
+        const originalMathRandom = Math.random;
+        Math.random = () => 0;
+        app.selectNextPerson();
+        Math.random = () => 0.5;
+        app.selectNextPerson();
+        Math.random = () => 0.9;
+        app.selectNextPerson();
+        Math.random = originalMathRandom;
+        
+        t.mock.method(app.mailSystem,'write');
+        t.mock.method(app.mailSystem,'send');
+        Math.random = () => 0.7;
+        app.notifySelected();
+       
+        let call_write = app.mailSystem.write.mock.calls[0];
+        let call_send = app.mailSystem.send.mock.calls[0];
+        
+        assert.deepStrictEqual(call_send.arguments,['John','Congrats, John!']);
+        assert.deepStrictEqual(call_write.arguments,['John']);
+        assert.strictEqual(call_send.result,true);
+        assert.strictEqual(call_write.result,'Congrats, John!');
+
+        call_write = app.mailSystem.write.mock.calls[1];
+        call_send = app.mailSystem.send.mock.calls[1];
+
+        assert.deepStrictEqual(call_send.arguments,['Jane','Congrats, Jane!']);
+        assert.deepStrictEqual(call_write.arguments,['Jane']);
+        assert.strictEqual(call_send.result,true);
+        assert.strictEqual(call_write.result,'Congrats, Jane!');
+
+        call_write = app.mailSystem.write.mock.calls[2];
+        call_send = app.mailSystem.send.mock.calls[2];
+
+        assert.deepStrictEqual(call_send.arguments,['Doe','Congrats, Doe!']);
+        assert.deepStrictEqual(call_write.arguments,['Doe']);
+        assert.strictEqual(call_send.result,true);
+        assert.strictEqual(call_write.result,'Congrats, Doe!');
+
+        Math.random = () => 0.3;
+        app.notifySelected();
+        
+        call_write = app.mailSystem.write.mock.calls[3];
+        call_send = app.mailSystem.send.mock.calls[3];
+        
+        assert.deepStrictEqual(call_send.arguments,['John','Congrats, John!']);
+        assert.deepStrictEqual(call_write.arguments,['John']);
+        assert.strictEqual(call_send.result,false);
+        assert.strictEqual(call_write.result,'Congrats, John!');
+
+        call_write = app.mailSystem.write.mock.calls[4];
+        call_send = app.mailSystem.send.mock.calls[4];
+
+        assert.deepStrictEqual(call_send.arguments,['Jane','Congrats, Jane!']);
+        assert.deepStrictEqual(call_write.arguments,['Jane']);
+        assert.strictEqual(call_send.result,false);
+        assert.strictEqual(call_write.result,'Congrats, Jane!');
+
+        call_write = app.mailSystem.write.mock.calls[5];
+        call_send = app.mailSystem.send.mock.calls[5];
+
+        assert.deepStrictEqual(call_send.arguments,['Doe','Congrats, Doe!']);
+        assert.deepStrictEqual(call_write.arguments,['Doe']);
+        assert.strictEqual(call_send.result,false);
+        assert.strictEqual(call_write.result,'Congrats, Doe!');
+        Math.random = originalMathRandom;
+        fs.unlink('name_list.txt', () => {}); // cleanup 
+});