diff --git a/lab2/main_test.js b/lab2/main_test.js
index 5034468e..6d8fb3f8 100644
--- a/lab2/main_test.js
+++ b/lab2/main_test.js
@@ -1,6 +1,98 @@
 const test = require('node:test');
 const assert = require('assert');
+const fs = require('fs');
+test.mock.method(fs, 'readFile', (a, b, callback) => callback(null, "Amy\nBenson\nCharlie"));
 const { Application, MailSystem } = require('./main');
 
-// TODO: write your tests here
-// Remember to use Stub, Mock, and Spy when necessary
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+// Remember to use Stub, Mock, and Spy when necessary
+test("Test MailSystem's write", () => {
+    const mailSys = new MailSystem();
+    // 1. test return type
+    assert.strictEqual(typeof mailSys.write("Amy"), "string");
+    // 2. validate legality of context returned
+    assert.strictEqual(mailSys.write("Amy"), "Congrats, Amy!");
+});
+
+test("Test MailSystem's send", (t) => {
+    const mailSys = new MailSystem();
+    // 1. test return type
+    assert.strictEqual(typeof mailSys.send("testing", "random test"), "boolean");
+    // 2. Asume that Math.random() works, check if the tested function provide a valid output (spy?)
+    t.mock.method(Math, "random", () => 1.0, { times: 5 });
+    for(let i = 0; i < 5; i++) {
+        assert.strictEqual(mailSys.send("testing", "random test"), true);
+    }
+    t.mock.method(Math, "random", () => 0.0, { times: 5 });
+    for(let i = 0; i < 5; i++) {
+        assert.strictEqual(mailSys.send("testing", "random test"), false);
+    }
+});
+
+test("Test Application's getNames", async () => {
+    // Stub inputs via mocking fs.writeFile
+    // Assume fs.writeFile works functionally, the tested function would have a correct behaviour.
+    const app = new Application();
+    const [people, selected] = await app.getNames();
+    assert.deepStrictEqual(people, ['Amy', 'Benson', 'Charlie']);
+    assert.deepStrictEqual(selected, []);
+});
+
+test("Test Application's getRandomPerson", (t) => {
+    const app = new Application();
+    // Stub
+    testcase = ['Amy', 'Benson', 'Charlie'];
+    app.people = testcase;
+    // Spy on output via mocking Math.random()
+    t.mock.method(Math, "random", () => 0.3, { times: 1 });
+    assert.strictEqual(app.getRandomPerson(), "Amy");
+    t.mock.method(Math, "random", () => 0.6, { times: 1 });
+    assert.strictEqual(app.getRandomPerson(), "Benson");
+    t.mock.method(Math, "random", () => 0.9, { times: 1 });
+    assert.strictEqual(app.getRandomPerson(), "Charlie");
+    // Spy on output via mocking Math.floor()
+    t.mock.method(Math, "floor", (_) => 0, { times: 1 });
+    assert.strictEqual(app.getRandomPerson(), "Amy");
+    t.mock.method(Math, "floor", (_) => 1, { times: 1 });
+    assert.strictEqual(app.getRandomPerson(), "Benson");
+    t.mock.method(Math, "floor", (_) => 2, { times: 1 });
+    assert.strictEqual(app.getRandomPerson(), "Charlie");
+});
+
+test("Test Application's selectNextPerson", (t) => {
+    const app = new Application();
+    //Stub
+    testcase = ['Amy', 'Benson', 'Charlie'];
+    app.people = testcase;
+    assert(app.people.includes(app.selectNextPerson()));
+    // Mock Implementation: call the selected person for five times
+    const proxy = t.mock.method(app, "getRandomPerson", ()=>app.selected[0], { times: 5 });
+    assert(app.people.includes(app.selectNextPerson()));
+    assert.strictEqual(proxy.mock.calls.length, 5);
+    for (let i = 0; i < 5; i++) {
+        assert.strictEqual(proxy.mock.calls[i].result, app.selected[0]);
+    }
+    // All the people are selected
+    assert(app.people.includes(app.selectNextPerson()));
+    assert.deepStrictEqual(app.people.toSorted(), app.selected.toSorted());
+    assert.strictEqual(app.selectNextPerson(), null);
+});
+
+test("Test Application's notifySelected", (t) => {
+    const app = new Application();
+    // Stub
+    testcase = ['Amy', 'Benson', 'Charlie'];
+    app.people = testcase;
+    app.selected = testcase;
+    // Mock cross-platform API
+    const ms_write = test.mock.method(app.mailSystem, "write");
+    const ms_send = test.mock.method(app.mailSystem, "send");
+    // Call tested function once and Examine info about function calls and data returned
+    app.notifySelected(); 
+    assert.strictEqual(ms_write.mock.calls.length, app.selected.length);
+    assert.strictEqual(ms_send.mock.calls.length, app.selected.length);
+    for (let i = 0; i < app.selected.length; i++) {
+        assert.strictEqual(ms_write.mock.calls[i].result, 'Congrats, ' + app.selected[i] + '!');
+        assert.strictEqual(ms_write.mock.calls[i].result, ms_send.mock.calls[i].arguments[1]);
+        assert.strictEqual(ms_send.mock.calls[i].arguments[0], ms_send.mock.calls[i].arguments[0]);
+    }
+});
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