diff --git a/backend/test-main.py b/backend/test-main.py
new file mode 100644
index 0000000..3784523
--- /dev/null
+++ b/backend/test-main.py
@@ -0,0 +1,215 @@
+import pytest
+import json
+from main import app, ANIMALS, USERS
+
+@pytest.fixture
+def client():
+    app.config['TESTING'] = True
+    with app.test_client() as client:
+        # Reset data before each test
+        global ANIMALS, USERS
+        ANIMALS = [
+            {
+                "id": 1,
+                "name": "Luna",
+                "species": "Dog",
+                "breed": "Labrador Mix",
+                "age": 2,
+                "personality": "Playful and energetic",
+                "image_path": "/images/luna.jpg",
+                "adoption_status": "Available"
+            },
+            {
+                "id": 2,
+                "name": "Oliver",
+                "species": "Cat",
+                "breed": "Tabby",
+                "age": 4,
+                "personality": "Independent but affectionate",
+                "image_path": "/images/oliver.jpg",
+                "adoption_status": "Available"
+            },
+            {
+                "id": 3,
+                "name": "Max",
+                "species": "Dog",
+                "breed": "German Shepherd",
+                "age": 3,
+                "personality": "Loyal and intelligent",
+                "image_path": "/images/max.jpg",
+                "adoption_status": "Available"
+            }
+        ]
+        USERS = [
+            {
+                "id": 1, 
+                "username": "admin",
+                "password": "admin123",
+                "email": "admin@example.com"
+            }
+        ]
+        yield client
+
+def test_homepage(client):
+    """Test that the homepage returns a 200 status code."""
+    response = client.get('/')
+    assert response.status_code == 200
+    assert b'Animal Shelter API' in response.data
+
+def test_register_user(client):
+    """Test user registration with valid data."""
+    response = client.post('/api/register', 
+                         json={
+                             'username': 'testuser',
+                             'password': 'password123',
+                             'email': 'test@example.com'
+                         })
+    assert response.status_code == 201
+    data = json.loads(response.data)
+    assert 'Registration successful' in data['message']
+    assert data['user_id'] == 2  # Should be the second user
+
+def test_register_duplicate_username(client):
+    """Test registration with a duplicate username."""
+    # First registration
+    client.post('/api/register', 
+               json={
+                   'username': 'testuser',
+                   'password': 'password123',
+                   'email': 'test@example.com'
+               })
+    
+    # Attempt to register with same username
+    response = client.post('/api/register', 
+                         json={
+                             'username': 'testuser',
+                             'password': 'different',
+                             'email': 'different@example.com'
+                         })
+    assert response.status_code == 409
+    data = json.loads(response.data)
+    assert 'Username already exists' in data['error']
+
+def test_register_missing_fields(client):
+    """Test registration with missing fields."""
+    response = client.post('/api/register', 
+                         json={
+                             'username': 'testuser',
+                             # Missing password and email
+                         })
+    assert response.status_code == 400
+    data = json.loads(response.data)
+    assert 'All fields are required' in data['error']
+
+def test_login_success(client):
+    """Test successful login."""
+    response = client.post('/api/login',
+                         json={
+                             'username': 'admin',
+                             'password': 'admin123'
+                         })
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert 'Login successful' in data['message']
+    assert data['username'] == 'admin'
+
+def test_login_incorrect_password(client):
+    """Test login with incorrect password."""
+    response = client.post('/api/login',
+                         json={
+                             'username': 'admin',
+                             'password': 'wrong_password'
+                         })
+    assert response.status_code == 401
+    data = json.loads(response.data)
+    assert 'Invalid username or password' in data['error']
+
+def test_login_nonexistent_user(client):
+    """Test login with a username that doesn't exist."""
+    response = client.post('/api/login',
+                         json={
+                             'username': 'nonexistent',
+                             'password': 'anything'
+                         })
+    assert response.status_code == 401
+    data = json.loads(response.data)
+    assert 'Invalid username or password' in data['error']
+
+def test_get_animals(client):
+    """Test getting all available animals."""
+    response = client.get('/api/animals')
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert len(data) == 3
+    assert data[0]['name'] == 'Luna'
+    assert data[1]['name'] == 'Oliver'
+    assert data[2]['name'] == 'Max'
+
+def test_get_animal_details(client):
+    """Test getting details for a specific animal."""
+    response = client.get('/api/animals/2')
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert data['name'] == 'Oliver'
+    assert data['species'] == 'Cat'
+    assert data['breed'] == 'Tabby'
+
+def test_get_nonexistent_animal(client):
+    """Test getting details for an animal that doesn't exist."""
+    response = client.get('/api/animals/999')
+    assert response.status_code == 404
+    data = json.loads(response.data)
+    assert 'Animal not found' in data['error']
+
+def test_adopt_animal(client):
+    """Test adopting an animal."""
+    response = client.post('/api/animals/1/adopt',
+                         json={
+                             'user_id': 1
+                         })
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert 'Adoption successful' in data['message']
+    assert data['animal']['adoption_status'] == 'Adopted'
+    
+    # Check that the animal is no longer available
+    response = client.get('/api/animals')
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert len(data) == 2  # Only 2 animals should now be available
+    
+def test_adopt_already_adopted_animal(client):
+    """Test trying to adopt an animal that's already adopted."""
+    # First adoption
+    client.post('/api/animals/1/adopt', json={'user_id': 1})
+    
+    # Attempt second adoption
+    response = client.post('/api/animals/1/adopt', json={'user_id': 1})
+    assert response.status_code == 400
+    data = json.loads(response.data)
+    assert 'Animal not available for adoption' in data['error']
+
+def test_animal_search(client):
+    """Test searching for animals with filters."""
+    # Search by species
+    response = client.get('/api/animals/search?species=Dog')
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert len(data) == 2
+    assert all(animal['species'] == 'Dog' for animal in data)
+    
+    # Search by age range
+    response = client.get('/api/animals/search?min_age=3&max_age=4')
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert len(data) == 2
+    assert all(3 <= animal['age'] <= 4 for animal in data)
+    
+    # Combined search
+    response = client.get('/api/animals/search?species=Cat&min_age=3')
+    assert response.status_code == 200
+    data = json.loads(response.data)
+    assert len(data) == 1
+    assert data[0]['name'] == 'Oliver'
+    assert data[0]['species'] == 'Cat'
+    assert data[0]['age'] == 4