diff --git a/frontend/src/components/CountDown/CountDown.test.tsx b/frontend/src/components/CountDown/CountDown.test.tsx
new file mode 100644
index 000000000..36aa951f6
--- /dev/null
+++ b/frontend/src/components/CountDown/CountDown.test.tsx
@@ -0,0 +1,117 @@
+import { render, screen, waitFor } from "@testing-library/react";
+import { beforeEach, describe, it, expect, vi, Mock } from "vitest";
+import CountDown from "./CountDown";
+import Timer from "@/util/timer";
+
+// Mock the Timer utility
+vi.mock("@/util/timer", () => ({
+    __esModule: true,
+    default: vi.fn(),
+}));
+
+const MockedTimer = Timer as Mock;
+
+describe("CountDown", () => {
+    beforeEach(() => {
+        // Clear all mocks before each test
+        vi.clearAllMocks();
+    });
+
+    it("should display the initial countdown value", () => {
+        render(<CountDown duration={10} />);
+
+        const score = screen.getByText("10");
+        expect(document.body.contains(score)).toBe(true);
+    });
+
+    it("should start the timer when running is true", async () => {
+        const mockTimer = vi.fn();
+        MockedTimer.mockImplementation(mockTimer);
+
+        render(<CountDown duration={10} running={true} />);
+
+        expect(mockTimer).toHaveBeenCalled();
+    });
+
+    it("should not start the timer when running is false", () => {
+        const mockTimer = vi.fn();
+        MockedTimer.mockImplementation(mockTimer);
+
+        render(<CountDown duration={10} running={false} />);
+
+        expect(mockTimer).not.toHaveBeenCalled();
+    });
+
+    it("should update the countdown value as the timer progresses", async () => {
+        let onTickCallback: (time: number) => void;
+        MockedTimer.mockImplementation(({ onTick }) => {
+            onTickCallback = onTick;
+            return vi.fn();
+        });
+
+        render(<CountDown duration={10} running={true} />);
+
+        await waitFor(() => {
+            const score = screen.getByText("10");
+            expect(document.body.contains(score)).toBe(true);
+        });
+
+        // Simulate timer ticks
+        onTickCallback!(5);
+        await waitFor(() => {
+            const score = screen.getByText("5");
+            expect(document.body.contains(score)).toBe(true);
+        });
+
+        onTickCallback!(9.5);
+        await waitFor(() => {
+            const score = screen.getByText("1");
+            expect(document.body.contains(score)).toBe(true);
+        });
+    });
+
+    it("should display 0 when the timer finishes", async () => {
+        let onFinishCallback: () => void;
+        MockedTimer.mockImplementation(({ onFinish }) => {
+            onFinishCallback = onFinish;
+            return vi.fn();
+        });
+
+        render(<CountDown duration={10} running={true} />);
+
+        await waitFor(() => {
+            const score = screen.getByText("10");
+            expect(document.body.contains(score)).toBe(true);
+        });
+
+        // Simulate timer finish
+        onFinishCallback!();
+        await waitFor(() => {
+            const score = screen.getByText("0");
+            expect(document.body.contains(score)).toBe(true);
+        });
+    });
+
+    it("should apply the correct classes based on the state", async () => {
+        const firstContainer = render(<CountDown duration={3} running={true} />);
+        let firstHeading = firstContainer.getByText("3");
+
+        MockedTimer.mockImplementation(({ onFinish }) => {
+            onFinish();
+            return vi.fn();
+        });
+
+        const secondContainer = render(<CountDown duration={5} running={true} />);
+
+        const secondHeading = secondContainer.getByText("0");
+
+        // First countdown should be active and not zero
+        expect(firstHeading.classList.contains('aha__count-down')).toBe(true);
+        expect(firstHeading.classList.contains('active')).toBe(true);
+        expect(firstHeading.classList.contains('zero')).toBe(false);
+
+        // Second countdown should be active and zero
+        expect(secondHeading.classList.contains('zero')).toBe(true);
+    });
+
+});
\ No newline at end of file
diff --git a/frontend/src/components/CountDown/CountDown.jsx b/frontend/src/components/CountDown/CountDown.tsx
similarity index 73%
rename from frontend/src/components/CountDown/CountDown.jsx
rename to frontend/src/components/CountDown/CountDown.tsx
index cef794f65..bee6f8b70 100644
--- a/frontend/src/components/CountDown/CountDown.jsx
+++ b/frontend/src/components/CountDown/CountDown.tsx
@@ -2,8 +2,13 @@ import React, { useState, useEffect } from "react";
 import Timer from "@/util/timer";
 import classNames from "classnames";
 
+interface CountDownProps {
+    duration: number;
+    running?: boolean;
+}
+
 // CountDown to zero
-const CountDown = ({ duration, running = true }) => {
+const CountDown = ({ duration, running = true }: CountDownProps) => {
     // automatic timer
     const [time, setTime] = useState(0);
     const [zero, setZero] = useState(false);
@@ -16,12 +21,8 @@ const CountDown = ({ duration, running = true }) => {
         // start time when running
         return Timer({
             duration,
-            onTick: (t) => {
-                setTime(Math.min(t, duration));
-            },
-            onFinish: () => {
-                setZero(true);
-            },
+            onTick: (t) => setTime(Math.min(t, duration)),
+            onFinish: () => setZero(true),
         });
     }, [duration, running]);
 
diff --git a/frontend/src/stories/CountDown.stories.jsx b/frontend/src/stories/CountDown.stories.jsx
new file mode 100644
index 000000000..4559525c1
--- /dev/null
+++ b/frontend/src/stories/CountDown.stories.jsx
@@ -0,0 +1,25 @@
+import CountDown from "../components/CountDown/CountDown";
+
+export default {
+    title: "CountDown",
+    component: CountDown,
+    parameters: {
+        layout: "fullscreen",
+    },
+};
+
+export const Default = {
+    args: {
+        duration: 3,
+        running: true,
+    },
+    decorators: [
+        (Story) => (
+            <div
+                style={{ width: "100%", height: "100%", backgroundColor: "#666", padding: "1rem" }}
+            >
+                <Story />
+            </div>
+        ),
+    ],
+};
\ No newline at end of file
diff --git a/frontend/src/util/timer.test.ts b/frontend/src/util/timer.test.ts
new file mode 100644
index 000000000..c074e150f
--- /dev/null
+++ b/frontend/src/util/timer.test.ts
@@ -0,0 +1,136 @@
+import { beforeEach, afterEach, describe, it, expect, vi } from 'vitest';
+import Timer from './timer';
+
+describe('Timer', () => {
+    let originalRequestAnimationFrame: any;
+    let now = 0;
+
+    beforeEach(() => {
+        // Use fake timers
+        vi.useFakeTimers();
+        now = 0;
+        vi.spyOn(performance, 'now').mockImplementation(() => now);
+
+        // Mock requestAnimationFrame
+        originalRequestAnimationFrame = window.requestAnimationFrame;
+        window.requestAnimationFrame = (cb) => {
+            setTimeout(() => {
+                now += 1000 / 60; // Simulate 60fps
+                cb(performance.now());
+            }, 1000 / 60);
+        };
+    });
+
+    afterEach(() => {
+        // Clear all timers and mocks
+        vi.clearAllTimers();
+        vi.restoreAllMocks();
+        window.requestAnimationFrame = originalRequestAnimationFrame;
+    });
+
+    it('should call onTick at intervals', () => {
+        const onTick = vi.fn();
+        const duration = 2;
+        const interval = 0.5;
+        const stop = Timer({
+            duration,
+            onTick,
+            interval,
+        });
+        // The number of ticks should be ceil(duration / interval) - 1
+        // as there is no tick when it finishes
+        const expectedTicks = Math.ceil(duration / interval) - 1;
+
+        // Advance the timer by 3 seconds
+        vi.advanceTimersByTime(3000);
+
+        // Check that onTick was called the correct number of times
+        expect(onTick).toHaveBeenCalledTimes(expectedTicks);
+
+        stop();
+    });
+
+    it('should call onFinish when the duration is reached', () => {
+        const onFinish = vi.fn();
+        const duration = 1;
+        const stop = Timer({
+            duration,
+            onFinish,
+        });
+
+        // Advance the timer by 2 seconds
+        vi.advanceTimersByTime(2000);
+
+        // Check that onFinish was called once
+        expect(onFinish).toHaveBeenCalledTimes(1);
+
+        stop();
+    });
+
+    it('should stop the timer when stop function is called', () => {
+        const onTick = vi.fn();
+        const duration = 2;
+        const interval = 0.5;
+        const stop = Timer({
+            duration,
+            onTick,
+            interval,
+        });
+
+        // Advance the timer by 1 second
+        vi.advanceTimersByTime(1000);
+
+        // Stop the timer
+        stop();
+
+        // Advance the timer by another 1 second
+        vi.advanceTimersByTime(1000);
+
+        // Check that onTick was called only for the first second
+        expect(onTick).toHaveBeenCalledTimes(2); // Should be called twice before stopping
+
+        stop();
+    });
+
+    it('should correctly handle the initial time parameter', () => {
+        const onTick = vi.fn();
+        const onFinish = vi.fn();
+        const duration = 3;
+        const interval = 0.5;
+        const time = 1;
+        const stop = Timer({
+            time,
+            duration,
+            onFinish,
+            onTick,
+            interval,
+        });
+
+        // Advance the timer by 500ms
+        vi.advanceTimersByTime(500);
+
+        expect(onFinish).not.toHaveBeenCalled(); // Should not have finished yet
+        expect(onTick).toHaveBeenCalledTimes(1); // Should have ticked once
+
+        // Advance the timer by another 500ms
+        vi.advanceTimersByTime(500);
+
+        expect(onFinish).not.toHaveBeenCalled(); // Should not have finished yet
+        expect(onTick).toHaveBeenCalledTimes(2); // Should have ticked twice
+
+        // Advance the timer by another 500ms
+        vi.advanceTimersByTime(500);
+
+        expect(onFinish).not.toHaveBeenCalled(); // Should not have finished yet
+        expect(onTick).toHaveBeenCalledTimes(3); // Should have ticked twice
+
+        // Advance the timer by another 500ms
+        vi.advanceTimersByTime(500);
+
+        // Check that onFinish was called once
+        expect(onFinish).toHaveBeenCalledTimes(1);
+        expect(onTick).toHaveBeenCalledTimes(3); // No extra tick after finishing
+        
+        stop();
+    });
+});
\ No newline at end of file
diff --git a/frontend/src/util/timer.js b/frontend/src/util/timer.ts
similarity index 67%
rename from frontend/src/util/timer.js
rename to frontend/src/util/timer.ts
index e3978568a..038304594 100644
--- a/frontend/src/util/timer.js
+++ b/frontend/src/util/timer.ts
@@ -1,3 +1,18 @@
+/**
+ * OnTick callback type
+ * @param time - current time in seconds
+ * @param delta - time since last tick in seconds
+ */
+type TOnTick = (time: number, delta: number) => void;
+
+interface TimerParams {
+    time?: number;          // initial time in seconds
+    duration: number;       // duration in seconds
+    onTick?: TOnTick;
+    onFinish?: () => void;
+    interval?: number;
+}
+
 // Timer component with callback
 export const Timer = ({
     time = 0,
@@ -5,12 +20,12 @@ export const Timer = ({
     onTick,
     onFinish,
     interval = 0.1,
-}) => {
+}: TimerParams) => {
     let lastTimestamp = performance.now();
     let lastTime = time;
     let running = true;
 
-    const callback = (timestamp) => {
+    const callback = (timestamp: number) => {
         if (!running) {
             return;
         }