diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 6381504..6777f4f 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -19,8 +19,66 @@ on:
     - cron: '0 3 * * 0'
 
 jobs:
-  build-and-deploy:
+  # ========================================================================
+  # Job to run unit tests.
+  # ========================================================================
+  test:
+    name: Run Linters and Tests
     runs-on: ubuntu-latest
+    steps:
+      # Checks out the repo under $GITHUB_WORKSPACE
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      # Sets up Python 3.12 environment
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: '3.12'
+          
+      # Cache pip dependencies for faster reruns
+      - name: Cache pip dependencies
+        uses: actions/cache@v3
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements*.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
+
+      - name: Install dependencies
+        working-directory: ./backend
+        run: |
+          python -m pip install --upgrade pip
+          pip install -r requirements.txt
+          pip install -r requirements-dev.txt
+
+      - name: Lint with Ruff
+        working-directory: ./backend
+        run: |
+          ruff check .
+
+      - name: Check formatting with Black
+        working-directory: ./backend
+        run: |
+          black --check .
+
+      - name: Run Pytest
+        working-directory: ./backend
+        run: |
+          pytest
+
+  # ========================================================================
+  # Job to build and deploy the Docker image to mara.
+  # ========================================================================
+  build-and-deploy:
+    name: Build and Deploy
+    runs-on: ubuntu-latest
+    needs: test # Ensure tests pass before deploying
+
+    # Only run this job if triggered by a push to main or manual dispatch/schedule
+    # This prevents it running for PRs (eventually)
+    if: github.event_name == 'push' || github.event_name == 'workflow_dispatch' || github.event_name == 'schedule'
+
     steps:
       # Checks out the repo under $GITHUB_WORKSPACE
       - name: Checkout code
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..7581cbf
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,7 @@
+{
+    "python.testing.pytestArgs": [
+        "backend"
+    ],
+    "python.testing.unittestEnabled": false,
+    "python.testing.pytestEnabled": true
+}
\ No newline at end of file
diff --git a/backend/core/__pycache__/celery_app.cpython-312.pyc b/backend/core/__pycache__/celery_app.cpython-312.pyc
index 8919cbe..ed5aaec 100644
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diff --git a/backend/core/__pycache__/config.cpython-312.pyc b/backend/core/__pycache__/config.cpython-312.pyc
index 3a175ae..1ae3b10 100644
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diff --git a/backend/core/config.py b/backend/core/config.py
index 80c6211..05f3642 100644
--- a/backend/core/config.py
+++ b/backend/core/config.py
@@ -3,12 +3,14 @@ from pydantic_settings import BaseSettings
 from pydantic import Field # Import Field for potential default values if needed
 import os
 
+DOTENV_PATH = os.path.join(os.path.dirname(__file__), "../.env")
+
 class Settings(BaseSettings):
     # Database settings - reads DB_URL from environment or .env
-    DB_URL: str
+    DB_URL: str = "postgresql://maia:maia@localhost:5432/maia"
 
     # Redis settings - reads REDIS_URL from environment or .env, also used for Celery.
-    REDIS_URL: str
+    REDIS_URL: str ="redis://localhost:6379/0"
 
     # JWT settings - reads from environment or .env
     JWT_ALGORITHM: str = "HS256"
@@ -22,7 +24,7 @@ class Settings(BaseSettings):
 
     class Config:
         # Tell pydantic-settings to load variables from a .env file
-        env_file = '.env'
+        env_file = DOTENV_PATH
         env_file_encoding = 'utf-8'
         extra = 'ignore'
 
diff --git a/backend/modules/admin/__pycache__/api.cpython-312.pyc b/backend/modules/admin/__pycache__/api.cpython-312.pyc
index e2753a4..06c11ba 100644
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diff --git a/backend/modules/calendar/__pycache__/api.cpython-312.pyc b/backend/modules/calendar/__pycache__/api.cpython-312.pyc
index 1465036..b276969 100644
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diff --git a/backend/modules/calendar/__pycache__/models.cpython-312.pyc b/backend/modules/calendar/__pycache__/models.cpython-312.pyc
index 31f3ae1..f86f1e9 100644
Binary files a/backend/modules/calendar/__pycache__/models.cpython-312.pyc and b/backend/modules/calendar/__pycache__/models.cpython-312.pyc differ
diff --git a/backend/modules/calendar/__pycache__/schemas.cpython-312.pyc b/backend/modules/calendar/__pycache__/schemas.cpython-312.pyc
index 829083a..cbfbd31 100644
Binary files a/backend/modules/calendar/__pycache__/schemas.cpython-312.pyc and b/backend/modules/calendar/__pycache__/schemas.cpython-312.pyc differ
diff --git a/backend/modules/calendar/api.py b/backend/modules/calendar/api.py
index bdd0700..81ecc15 100644
--- a/backend/modules/calendar/api.py
+++ b/backend/modules/calendar/api.py
@@ -1,5 +1,5 @@
 # modules/calendar/api.py
-from fastapi import APIRouter, Depends
+from fastapi import APIRouter, Depends, status
 from sqlalchemy.orm import Session
 from datetime import datetime
 from typing import List, Optional
@@ -12,7 +12,7 @@ from modules.calendar.service import create_calendar_event, get_calendar_event_b
 
 router = APIRouter(prefix="/calendar", tags=["calendar"])
 
-@router.post("/events", response_model=CalendarEventResponse)
+@router.post("/events", response_model=CalendarEventResponse, status_code=status.HTTP_201_CREATED)
 def create_event(
     event: CalendarEventCreate,
     user: User = Depends(get_current_user),
diff --git a/backend/modules/calendar/models.py b/backend/modules/calendar/models.py
index 9167a15..17cde49 100644
--- a/backend/modules/calendar/models.py
+++ b/backend/modules/calendar/models.py
@@ -1,5 +1,5 @@
 # modules/calendar/models.py
-from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, JSON # Add JSON
+from sqlalchemy import Column, Integer, String, DateTime, ForeignKey, JSON, Boolean # Add Boolean
 from sqlalchemy.orm import relationship
 from core.database import Base
 
@@ -12,6 +12,7 @@ class CalendarEvent(Base):
     start = Column(DateTime, nullable=False)
     end = Column(DateTime)
     location = Column(String)
+    all_day = Column(Boolean, default=False) # Add all_day column
     tags = Column(JSON)
     color = Column(String) # hex code for color
     user_id = Column(Integer, ForeignKey("users.id"), nullable=False)  # <-- Relationship
diff --git a/backend/modules/calendar/schemas.py b/backend/modules/calendar/schemas.py
index ed04949..760da49 100644
--- a/backend/modules/calendar/schemas.py
+++ b/backend/modules/calendar/schemas.py
@@ -11,6 +11,7 @@ class CalendarEventBase(BaseModel):
     end: Optional[datetime] = None
     location: Optional[str] = None
     color: Optional[str] = None # Assuming color exists
+    all_day: Optional[bool] = None # Add all_day field
     tags: Optional[List[str]] = None # Add optional tags
 
     @field_validator('tags', mode='before')
@@ -32,6 +33,7 @@ class CalendarEventUpdate(BaseModel):
     end: Optional[datetime] = None
     location: Optional[str] = None
     color: Optional[str] = None
+    all_day: Optional[bool] = None # Add all_day field
     tags: Optional[List[str]] = None # Add optional tags for update
 
     @field_validator('tags', mode='before')
diff --git a/backend/requirements-dev.txt b/backend/requirements-dev.txt
new file mode 100644
index 0000000..f991949
--- /dev/null
+++ b/backend/requirements-dev.txt
@@ -0,0 +1,4 @@
+pytest
+pytest-cov # For checking test coverage (optional)
+ruff # Or flake8, pylint etc. for linting
+black # For code formatting checks
\ No newline at end of file
diff --git a/backend/tests/__pycache__/test_admin.cpython-312-pytest-8.3.5.pyc b/backend/tests/__pycache__/test_admin.cpython-312-pytest-8.3.5.pyc
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diff --git a/backend/tests/__pycache__/test_auth.cpython-312-pytest-8.3.5.pyc b/backend/tests/__pycache__/test_auth.cpython-312-pytest-8.3.5.pyc
index 9470be8..9d0b1dc 100644
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diff --git a/backend/tests/__pycache__/test_calendar.cpython-312-pytest-8.3.5.pyc b/backend/tests/__pycache__/test_calendar.cpython-312-pytest-8.3.5.pyc
index c04a8ee..c5e6041 100644
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diff --git a/backend/tests/__pycache__/test_main.cpython-312-pytest-8.3.5.pyc b/backend/tests/__pycache__/test_main.cpython-312-pytest-8.3.5.pyc
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diff --git a/backend/tests/__pycache__/test_nlp.cpython-312-pytest-8.3.5.pyc b/backend/tests/__pycache__/test_nlp.cpython-312-pytest-8.3.5.pyc
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index 0000000..454d395
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diff --git a/backend/tests/__pycache__/test_todo.cpython-312-pytest-8.3.5.pyc b/backend/tests/__pycache__/test_todo.cpython-312-pytest-8.3.5.pyc
new file mode 100644
index 0000000..c7a6b6e
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diff --git a/backend/tests/helpers/__pycache__/generators.cpython-312.pyc b/backend/tests/helpers/__pycache__/generators.cpython-312.pyc
index 636ef09..71548d4 100644
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diff --git a/backend/tests/helpers/generators.py b/backend/tests/helpers/generators.py
index 25c9469..9ed550d 100644
--- a/backend/tests/helpers/generators.py
+++ b/backend/tests/helpers/generators.py
@@ -8,13 +8,14 @@ from modules.auth.models import User
 from modules.auth.security import authenticate_user, create_access_token, create_refresh_token, hash_password
 from modules.auth.schemas import UserRole
 from tests.conftest import fake
+from typing import Optional # Import Optional
 
 
-def create_user(db: Session, is_admin: bool = False) -> User:
+def create_user(db: Session, is_admin: bool = False, username: Optional[str] = None) -> User:
     unhashed_password = fake.password()
     _user = User(
         name=fake.name(),
-        username=fake.user_name(),
+        username=username or fake.user_name(), # Use provided username or generate one
         hashed_password=hash_password(unhashed_password),
         uuid=uuid_pkg.uuid4(),
         role=UserRole.ADMIN if is_admin else UserRole.USER,
diff --git a/backend/tests/test_admin.py b/backend/tests/test_admin.py
new file mode 100644
index 0000000..3885fd2
--- /dev/null
+++ b/backend/tests/test_admin.py
@@ -0,0 +1,79 @@
+import pytest
+from fastapi import status
+from fastapi.testclient import TestClient
+from sqlalchemy.orm import Session
+from unittest.mock import patch
+
+from tests.helpers import generators
+from modules.auth.models import UserRole
+
+# Test admin routes require admin privileges
+
+def test_read_admin_unauthorized(client: TestClient) -> None:
+    """Test accessing admin route without authentication."""
+    response = client.get("/api/admin/")
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_read_admin_forbidden(db: Session, client: TestClient) -> None:
+    """Test accessing admin route as a non-admin user."""
+    user, password = generators.create_user(db, is_admin=False) # Use is_admin=False
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+
+    response = client.get("/api/admin/", headers={"Authorization": f"Bearer {access_token}"})
+    assert response.status_code == status.HTTP_403_FORBIDDEN
+
+def test_read_admin_success(db: Session, client: TestClient) -> None:
+    """Test accessing admin route as an admin user."""
+    admin_user, password = generators.create_user(db, is_admin=True) # Use is_admin=True
+    login_rsp = generators.login(db, admin_user.username, password)
+    access_token = login_rsp["access_token"]
+
+    response = client.get("/api/admin/", headers={"Authorization": f"Bearer {access_token}"})
+    assert response.status_code == status.HTTP_200_OK
+    assert response.json() == {"message": "Admin route"}
+
+@patch("modules.admin.api.cleardb.delay") # Mock the celery task
+def test_clear_db_soft(mock_cleardb_delay, db: Session, client: TestClient) -> None:
+    """Test soft clearing the database as admin."""
+    admin_user, password = generators.create_user(db, is_admin=True) # Use is_admin=True
+    login_rsp = generators.login(db, admin_user.username, password)
+    access_token = login_rsp["access_token"]
+
+    response = client.post(
+        "/api/admin/cleardb",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json={"hard": False}
+    )
+    assert response.status_code == status.HTTP_200_OK
+    assert response.json() == {"message": "Clearing database in the background", "hard": False}
+    mock_cleardb_delay.assert_called_once_with(False)
+
+@patch("modules.admin.api.cleardb.delay") # Mock the celery task
+def test_clear_db_hard(mock_cleardb_delay, db: Session, client: TestClient) -> None:
+    """Test hard clearing the database as admin."""
+    admin_user, password = generators.create_user(db, is_admin=True) # Use is_admin=True
+    login_rsp = generators.login(db, admin_user.username, password)
+    access_token = login_rsp["access_token"]
+
+    response = client.post(
+        "/api/admin/cleardb",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json={"hard": True}
+    )
+    assert response.status_code == status.HTTP_200_OK
+    assert response.json() == {"message": "Clearing database in the background", "hard": True}
+    mock_cleardb_delay.assert_called_once_with(True)
+
+def test_clear_db_forbidden(db: Session, client: TestClient) -> None:
+    """Test clearing the database as a non-admin user."""
+    user, password = generators.create_user(db, is_admin=False) # Use is_admin=False
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+
+    response = client.post(
+        "/api/admin/cleardb",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json={"hard": False}
+    )
+    assert response.status_code == status.HTTP_403_FORBIDDEN
diff --git a/backend/tests/test_auth.py b/backend/tests/test_auth.py
index 10813d2..22c0115 100644
--- a/backend/tests/test_auth.py
+++ b/backend/tests/test_auth.py
@@ -61,8 +61,8 @@ def test_refresh_token(db: Session, client: TestClient) -> None:
 
     response = client.post(
         "/api/auth/refresh",
-        headers={"Authorization": f"Bearer {access_token}"},
-        cookies={"refresh_token": refresh_token},
+        headers={"Authorization": f"Bearer {access_token}", "Content-Type": "application/json"},
+        json={"refresh_token": refresh_token},
     )
     assert response.status_code == status.HTTP_200_OK
 
@@ -80,8 +80,8 @@ def test_logout(db: Session, client: TestClient) -> None:
 
     response = client.post(
         "/api/auth/logout",
-        headers={"Authorization": f"Bearer {access_token}"},
-        cookies={"refresh_token": refresh_token},
+        headers={"Authorization": f"Bearer {access_token}", "Content-Type": "application/json"},
+        json={"refresh_token": refresh_token},
     )
     assert response.status_code == status.HTTP_200_OK
 
@@ -98,7 +98,8 @@ def test_logout(db: Session, client: TestClient) -> None:
 
     response = client.post(
         "/api/auth/refresh",
-        cookies={"refresh_token": refresh_token},
+        headers={"Authorization": f"Bearer {access_token}", "Content-Type": "application/json"},
+        json={"refresh_token": refresh_token},
     )
     assert response.status_code == status.HTTP_401_UNAUTHORIZED
 
@@ -177,4 +178,53 @@ def test_delete_user(db: Session, client: TestClient) -> None:
     # Verify that the user is deleted
     deleted_user = db.query(User).filter(User.username == user.username).first()
     assert deleted_user is None
-    
\ No newline at end of file
+
+def test_get_user_forbidden(db: Session, client: TestClient) -> None:
+    """Test getting another user's profile (should be forbidden)."""
+    user1, password_user1 = generators.create_user(db, username="user1_get_forbidden")
+    user2, _ = generators.create_user(db, username="user2_get_forbidden")
+
+    # Log in as user1
+    login_rsp = generators.login(db, user1.username, password_user1)
+    access_token = login_rsp["access_token"]
+
+    # Try to get user2's profile
+    response = client.get(
+        f"/api/user/{user2.username}",
+        headers={"Authorization": f"Bearer {access_token}"},
+    )
+    assert response.status_code == status.HTTP_403_FORBIDDEN
+
+def test_update_user_forbidden(db: Session, client: TestClient) -> None:
+    """Test updating another user's profile (should be forbidden)."""
+    user1, password_user1 = generators.create_user(db, username="user1_update_forbidden")
+    user2, _ = generators.create_user(db, username="user2_update_forbidden")
+    new_name = fake.name()
+
+    # Log in as user1
+    login_rsp = generators.login(db, user1.username, password_user1)
+    access_token = login_rsp["access_token"]
+
+    # Try to update user2's profile
+    response = client.patch(
+        f"/api/user/{user2.username}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json={"name": new_name},
+    )
+    assert response.status_code == status.HTTP_403_FORBIDDEN
+
+def test_delete_user_forbidden(db: Session, client: TestClient) -> None:
+    """Test deleting another user's profile (should be forbidden)."""
+    user1, password_user1 = generators.create_user(db, username="user1_delete_forbidden")
+    user2, _ = generators.create_user(db, username="user2_delete_forbidden")
+
+    # Log in as user1
+    login_rsp = generators.login(db, user1.username, password_user1)
+    access_token = login_rsp["access_token"]
+
+    # Try to delete user2's profile
+    response = client.delete(
+        f"/api/user/{user2.username}",
+        headers={"Authorization": f"Bearer {access_token}"},
+    )
+    assert response.status_code == status.HTTP_403_FORBIDDEN
diff --git a/backend/tests/test_calendar.py b/backend/tests/test_calendar.py
index caba7ab..da0eec6 100644
--- a/backend/tests/test_calendar.py
+++ b/backend/tests/test_calendar.py
@@ -1,44 +1,389 @@
+import pytest
+from fastapi import status
 from fastapi.testclient import TestClient
 from sqlalchemy.orm import Session
+from datetime import datetime, timedelta
+
 from tests.helpers import generators
+from modules.calendar.models import CalendarEvent # Assuming model exists
+from tests.conftest import fake
+
+# Helper function to create an event payload
+def create_event_payload(start_offset_days=0, end_offset_days=1):
+    start_time = datetime.utcnow() + timedelta(days=start_offset_days)
+    end_time = datetime.utcnow() + timedelta(days=end_offset_days)
+    return {
+        "title": fake.sentence(nb_words=3),
+        "description": fake.text(),
+        "start": start_time.isoformat(), # Rename start_time to start
+        "end": end_time.isoformat(),     # Rename end_time to end
+        "all_day": fake.boolean(),
+    }
+
+# --- Test Create Event ---
+
+def test_create_event_unauthorized(client: TestClient) -> None:
+    """Test creating an event without authentication."""
+    payload = create_event_payload()
+    response = client.post("/api/calendar/events", json=payload)
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_create_event_success(db: Session, client: TestClient) -> None:
+    """Test creating a calendar event successfully."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+
+    response = client.post(
+        "/api/calendar/events",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json=payload
+    )
+    assert response.status_code == status.HTTP_201_CREATED # Change expected status to 201
+    data = response.json()
+    assert data["title"] == payload["title"]
+    assert data["description"] == payload["description"]
+    # Remove the '+ "Z"' as the API doesn't add it
+    assert data["start"] == payload["start"]
+    assert data["end"] == payload["end"]
+    assert data["all_day"] == payload["all_day"]
+    assert "id" in data
+    assert data["user_id"] == user.id
+
+    # Verify in DB
+    event_in_db = db.query(CalendarEvent).filter(CalendarEvent.id == data["id"]).first()
+    assert event_in_db is not None
+    assert event_in_db.user_id == user.id
+    assert event_in_db.title == payload["title"]
+
+# --- Test Get Events ---
+
+def test_get_events_unauthorized(client: TestClient) -> None:
+    """Test getting events without authentication."""
+    response = client.get("/api/calendar/events")
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_get_events_success(db: Session, client: TestClient) -> None:
+    """Test getting all calendar events for a user."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+
+    # Create a couple of events for the user
+    payload1 = create_event_payload(0, 1)
+    client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload1)
+    payload2 = create_event_payload(2, 3)
+    client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload2)
+
+    # Create an event for another user (should not be returned)
+    other_user, other_password = generators.create_user(db)
+    other_login_rsp = generators.login(db, other_user.username, other_password)
+    other_access_token = other_login_rsp["access_token"]
+    other_payload = create_event_payload(4, 5)
+    client.post("/api/calendar/events", headers={"Authorization": f"Bearer {other_access_token}"}, json=other_payload)
 
 
-def test_create_event(client: TestClient, db: Session) -> None:
-    user, unhashed_password = generators.create_user(db)
-    rsp = generators.login(db, user.username, unhashed_password)
-    access_token = rsp["access_token"]
-    refresh_token = rsp["refresh_token"]
-    
-    response = client.post("/api/calendar/events", 
-        json={
-            "title": "Test Event",
-            "start_time": "2024-03-20T15:00:00Z"
-        },
-        headers={"Authorization": f"Bearer {access_token}"},
-        cookies={"refresh_token": refresh_token},
+    response = client.get(
+        "/api/calendar/events",
+        headers={"Authorization": f"Bearer {access_token}"}
     )
-    assert response.status_code == 200
-    assert response.json()["title"] == "Test Event"
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert len(data) == 2
+    assert data[0]["title"] == payload1["title"]
+    assert data[1]["title"] == payload2["title"]
+    assert data[0]["user_id"] == user.id
+    assert data[1]["user_id"] == user.id
 
-def test_get_events(client: TestClient, db: Session) -> None:
-    user, unhashed_password = generators.create_user(db)
-    rsp = generators.login(db, user.username, unhashed_password)
-    access_token = rsp["access_token"]
-    refresh_token = rsp["refresh_token"]
-    
-    # Create an event to retrieve
-    client.post("/api/calendar/events", 
-        json={
-            "title": "Test Event",
-            "start_time": "2024-03-20T15:00:00Z"
-        },
+
+def test_get_events_filtered(db: Session, client: TestClient) -> None:
+    """Test getting filtered calendar events for a user."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+
+    # Create events
+    payload1 = create_event_payload(0, 1) # Today -> Tomorrow
+    client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload1)
+    payload2 = create_event_payload(5, 6) # In 5 days -> In 6 days
+    client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload2)
+    payload3 = create_event_payload(10, 11) # In 10 days -> In 11 days
+    client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload3)
+
+    # Filter for events starting within the next week
+    start_filter = datetime.utcnow().isoformat()
+    end_filter = (datetime.utcnow() + timedelta(days=7)).isoformat()
+
+    response = client.get(
+        "/api/calendar/events",
         headers={"Authorization": f"Bearer {access_token}"},
-        cookies={"refresh_token": refresh_token},
+        params={"start": start_filter, "end": end_filter}
     )
-    
-    response = client.get("/api/calendar/events", 
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert len(data) == 2 # Should get event 1 and 2
+    assert data[0]["title"] == payload1["title"]
+    assert data[1]["title"] == payload2["title"]
+
+    # Filter for events starting after 8 days
+    start_filter_late = (datetime.utcnow() + timedelta(days=8)).isoformat()
+    response = client.get(
+        "/api/calendar/events",
         headers={"Authorization": f"Bearer {access_token}"},
-        cookies={"refresh_token": refresh_token},
+        params={"start": start_filter_late}
     )
-    assert response.status_code == 200
-    assert len(response.json()) > 0
\ No newline at end of file
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert len(data) == 1 # Should get event 3
+    assert data[0]["title"] == payload3["title"]
+
+
+# --- Test Get Event By ID ---
+
+def test_get_event_by_id_unauthorized(db: Session, client: TestClient) -> None:
+    """Test getting a specific event without authentication."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload)
+    event_id = create_response.json()["id"]
+
+    response = client.get(f"/api/calendar/events/{event_id}")
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_get_event_by_id_success(db: Session, client: TestClient) -> None:
+    """Test getting a specific event successfully."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload)
+    event_id = create_response.json()["id"]
+
+    response = client.get(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token}"}
+    )
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert data["id"] == event_id
+    assert data["title"] == payload["title"]
+    assert data["user_id"] == user.id
+
+def test_get_event_by_id_not_found(db: Session, client: TestClient) -> None:
+    """Test getting a non-existent event."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    non_existent_id = 99999
+
+    response = client.get(
+        f"/api/calendar/events/{non_existent_id}",
+        headers={"Authorization": f"Bearer {access_token}"}
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+def test_get_event_by_id_forbidden(db: Session, client: TestClient) -> None:
+    """Test getting another user's event."""
+    user1, password_user1 = generators.create_user(db)
+    user2, password_user2 = generators.create_user(db)
+
+    # Log in as user1 and create an event
+    login_rsp1 = generators.login(db, user1.username, password_user1)
+    access_token1 = login_rsp1["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token1}"}, json=payload)
+    event_id = create_response.json()["id"]
+
+    # Log in as user2 and try to get user1's event
+    login_rsp2 = generators.login(db, user2.username, password_user2)
+    access_token2 = login_rsp2["access_token"]
+
+    response = client.get(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token2}"}
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND # Service layer returns 404 if user_id doesn't match
+
+# --- Test Update Event ---
+
+def test_update_event_unauthorized(db: Session, client: TestClient) -> None:
+    """Test updating an event without authentication."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload)
+    event_id = create_response.json()["id"]
+    update_payload = {"title": "Updated Title"}
+
+    response = client.patch(f"/api/calendar/events/{event_id}", json=update_payload)
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_update_event_success(db: Session, client: TestClient) -> None:
+    """Test updating an event successfully."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload)
+    assert create_response.status_code == status.HTTP_201_CREATED # Ensure creation check uses 201
+    event_id = create_response.json()["id"]
+
+    update_payload = {
+        "title": "Updated Title",
+        "description": "Updated description.",
+        "all_day": not payload["all_day"] # Toggle all_day
+    }
+
+    response = client.patch(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json=update_payload
+    )
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert data["id"] == event_id
+    assert data["title"] == update_payload["title"]
+    assert data["description"] == update_payload["description"]
+    assert data["all_day"] == update_payload["all_day"]
+    assert data["start"] == payload["start"] # Check correct field name 'start'
+    assert data["user_id"] == user.id
+
+    # Verify in DB
+    event_in_db = db.query(CalendarEvent).filter(CalendarEvent.id == event_id).first()
+    assert event_in_db is not None
+    assert event_in_db.title == update_payload["title"]
+    assert event_in_db.description == update_payload["description"]
+    assert event_in_db.all_day == update_payload["all_day"]
+
+def test_update_event_not_found(db: Session, client: TestClient) -> None:
+    """Test updating a non-existent event."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    non_existent_id = 99999
+    update_payload = {"title": "Updated Title"}
+
+    response = client.patch(
+        f"/api/calendar/events/{non_existent_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        json=update_payload
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+def test_update_event_forbidden(db: Session, client: TestClient) -> None:
+    """Test updating another user's event."""
+    user1, password_user1 = generators.create_user(db)
+    user2, password_user2 = generators.create_user(db)
+
+    # Log in as user1 and create an event
+    login_rsp1 = generators.login(db, user1.username, password_user1)
+    access_token1 = login_rsp1["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token1}"}, json=payload)
+    event_id = create_response.json()["id"]
+
+    # Log in as user2 and try to update user1's event
+    login_rsp2 = generators.login(db, user2.username, password_user2)
+    access_token2 = login_rsp2["access_token"]
+    update_payload = {"title": "Updated by User 2"}
+
+    response = client.patch(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token2}"},
+        json=update_payload
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND # Service layer returns 404 if user_id doesn't match
+
+# --- Test Delete Event ---
+
+def test_delete_event_unauthorized(db: Session, client: TestClient) -> None:
+    """Test deleting an event without authentication."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload)
+    event_id = create_response.json()["id"]
+
+    response = client.delete(f"/api/calendar/events/{event_id}")
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_delete_event_success(db: Session, client: TestClient) -> None:
+    """Test deleting an event successfully."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token}"}, json=payload)
+    assert create_response.status_code == status.HTTP_201_CREATED # Ensure creation check uses 201
+    event_id = create_response.json()["id"]
+
+    # Verify event exists before delete
+    event_in_db = db.query(CalendarEvent).filter(CalendarEvent.id == event_id).first()
+    assert event_in_db is not None
+
+    response = client.delete(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token}"}
+    )
+    assert response.status_code == status.HTTP_204_NO_CONTENT
+
+    # Verify event is deleted from DB
+    event_in_db = db.query(CalendarEvent).filter(CalendarEvent.id == event_id).first()
+    assert event_in_db is None
+
+    # Try getting the deleted event (should be 404)
+    get_response = client.get(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token}"}
+    )
+    assert get_response.status_code == status.HTTP_404_NOT_FOUND
+
+
+def test_delete_event_not_found(db: Session, client: TestClient) -> None:
+    """Test deleting a non-existent event."""
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    access_token = login_rsp["access_token"]
+    non_existent_id = 99999
+
+    response = client.delete(
+        f"/api/calendar/events/{non_existent_id}",
+        headers={"Authorization": f"Bearer {access_token}"}
+    )
+    # The service layer raises NotFound, which should result in 404
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+
+def test_delete_event_forbidden(db: Session, client: TestClient) -> None:
+    """Test deleting another user's event."""
+    user1, password_user1 = generators.create_user(db)
+    user2, password_user2 = generators.create_user(db)
+
+    # Log in as user1 and create an event
+    login_rsp1 = generators.login(db, user1.username, password_user1)
+    access_token1 = login_rsp1["access_token"]
+    payload = create_event_payload()
+    create_response = client.post("/api/calendar/events", headers={"Authorization": f"Bearer {access_token1}"}, json=payload)
+    event_id = create_response.json()["id"]
+
+    # Log in as user2 and try to delete user1's event
+    login_rsp2 = generators.login(db, user2.username, password_user2)
+    access_token2 = login_rsp2["access_token"]
+
+    response = client.delete(
+        f"/api/calendar/events/{event_id}",
+        headers={"Authorization": f"Bearer {access_token2}"}
+    )
+    # The service layer raises NotFound if user_id doesn't match, resulting in 404
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+    # Verify event still exists for user1
+    event_in_db = db.query(CalendarEvent).filter(CalendarEvent.id == event_id).first()
+    assert event_in_db is not None
+    assert event_in_db.user_id == user1.id
+
diff --git a/backend/tests/test_main.py b/backend/tests/test_main.py
new file mode 100644
index 0000000..2401a93
--- /dev/null
+++ b/backend/tests/test_main.py
@@ -0,0 +1,10 @@
+import pytest
+from fastapi.testclient import TestClient
+
+# No database needed for this simple test
+
+def test_health_check(client: TestClient):
+    """Test the health check endpoint."""
+    response = client.get("/api/health")
+    assert response.status_code == 200
+    assert response.json() == {"status": "ok"}
diff --git a/backend/tests/test_nlp.py b/backend/tests/test_nlp.py
new file mode 100644
index 0000000..28f39e3
--- /dev/null
+++ b/backend/tests/test_nlp.py
@@ -0,0 +1,218 @@
+import pytest
+from fastapi import status
+from fastapi.testclient import TestClient
+from sqlalchemy.orm import Session
+from unittest.mock import patch, MagicMock
+from datetime import datetime
+
+from tests.helpers import generators
+from modules.nlp.schemas import ProcessCommandRequest, ProcessCommandResponse
+from modules.nlp.models import MessageSender, ChatMessage # Import necessary models/enums
+
+# --- Mocks ---
+# Mock the external AI call and internal service functions
+@pytest.fixture(autouse=True)
+def mock_nlp_services():
+    with patch("modules.nlp.api.process_request") as mock_process, \
+         patch("modules.nlp.api.ask_ai") as mock_ask, \
+         patch("modules.nlp.api.save_chat_message") as mock_save, \
+         patch("modules.nlp.api.get_chat_history") as mock_get_history, \
+         patch("modules.nlp.api.create_calendar_event") as mock_create_event, \
+         patch("modules.nlp.api.get_calendar_events") as mock_get_events, \
+         patch("modules.nlp.api.update_calendar_event") as mock_update_event, \
+         patch("modules.nlp.api.delete_calendar_event") as mock_delete_event, \
+         patch("modules.nlp.api.todo_service.create_todo") as mock_create_todo, \
+         patch("modules.nlp.api.todo_service.get_todos") as mock_get_todos, \
+         patch("modules.nlp.api.todo_service.update_todo") as mock_update_todo, \
+         patch("modules.nlp.api.todo_service.delete_todo") as mock_delete_todo:
+        mocks = {
+            "process_request": mock_process,
+            "ask_ai": mock_ask,
+            "save_chat_message": mock_save,
+            "get_chat_history": mock_get_history,
+            "create_calendar_event": mock_create_event,
+            "get_calendar_events": mock_get_events,
+            "update_calendar_event": mock_update_event,
+            "delete_calendar_event": mock_delete_event,
+            "create_todo": mock_create_todo,
+            "get_todos": mock_get_todos,
+            "update_todo": mock_update_todo,
+            "delete_todo": mock_delete_todo,
+        }
+        yield mocks
+
+# --- Helper Function ---
+def _login_user(db: Session, client: TestClient):
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    return user, login_rsp["access_token"], login_rsp["refresh_token"]
+
+# --- Tests for /process-command ---
+
+def test_process_command_ask_ai(client: TestClient, db: Session, mock_nlp_services):
+    user, access_token, refresh_token = _login_user(db, client)
+    user_input = "What is the capital of France?"
+    mock_nlp_services["process_request"].return_value = {
+        "intent": "ask_ai",
+        "params": {"request": user_input},
+        "response_text": "Let me check that for you."
+    }
+    mock_nlp_services["ask_ai"].return_value = "The capital of France is Paris."
+
+    response = client.post(
+        "/api/nlp/process-command",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"user_input": user_input}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    assert response.json() == ProcessCommandResponse(responses=["Let me check that for you.", "The capital of France is Paris."]).model_dump()
+    # Verify save calls: user message, initial AI response, final AI answer
+    assert mock_nlp_services["save_chat_message"].call_count == 3
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.USER, text=user_input)
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.AI, text="Let me check that for you.")
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.AI, text="The capital of France is Paris.")
+    mock_nlp_services["ask_ai"].assert_called_once_with(request=user_input)
+
+def test_process_command_get_calendar(client: TestClient, db: Session, mock_nlp_services):
+    user, access_token, refresh_token = _login_user(db, client)
+    user_input = "What are my events today?"
+    mock_nlp_services["process_request"].return_value = {
+        "intent": "get_calendar_events",
+        "params": {"start": "2024-01-01T00:00:00Z", "end": "2024-01-01T23:59:59Z"}, # Example params
+        "response_text": "Okay, fetching your events."
+    }
+    # Mock the actual event model returned by the service
+    mock_event = MagicMock()
+    mock_event.title = "Team Meeting"
+    mock_event.start = datetime(2024, 1, 1, 10, 0, 0)
+    mock_event.end = datetime(2024, 1, 1, 11, 0, 0)
+    mock_nlp_services["get_calendar_events"].return_value = [mock_event]
+
+    response = client.post(
+        "/api/nlp/process-command",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"user_input": user_input}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    expected_responses = [
+        "Okay, fetching your events.",
+        "Here are the events:",
+        "- Team Meeting (2024-01-01 10:00 - 11:00)"
+    ]
+    assert response.json() == ProcessCommandResponse(responses=expected_responses).model_dump()
+    assert mock_nlp_services["save_chat_message"].call_count == 4 # User, Initial AI, Header, Event
+    mock_nlp_services["get_calendar_events"].assert_called_once()
+
+def test_process_command_add_todo(client: TestClient, db: Session, mock_nlp_services):
+    user, access_token, refresh_token = _login_user(db, client)
+    user_input = "Add buy milk to my list"
+    mock_nlp_services["process_request"].return_value = {
+        "intent": "add_todo",
+        "params": {"task": "buy milk"},
+        "response_text": "Adding it now."
+    }
+    # Mock the actual Todo model returned by the service
+    mock_todo = MagicMock()
+    mock_todo.task = "buy milk"
+    mock_todo.id = 1
+    mock_nlp_services["create_todo"].return_value = mock_todo
+
+    response = client.post(
+        "/api/nlp/process-command",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"user_input": user_input}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    expected_responses = ["Adding it now.", "Added TODO: 'buy milk' (ID: 1)."]
+    assert response.json() == ProcessCommandResponse(responses=expected_responses).model_dump()
+    assert mock_nlp_services["save_chat_message"].call_count == 3 # User, Initial AI, Confirmation AI
+    mock_nlp_services["create_todo"].assert_called_once()
+
+def test_process_command_clarification(client: TestClient, db: Session, mock_nlp_services):
+    user, access_token, refresh_token = _login_user(db, client)
+    user_input = "Delete the event"
+    clarification_text = "Which event do you mean? Please provide the ID."
+    mock_nlp_services["process_request"].return_value = {
+        "intent": "clarification_needed",
+        "params": {"request": user_input},
+        "response_text": clarification_text
+    }
+
+    response = client.post(
+        "/api/nlp/process-command",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"user_input": user_input}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    assert response.json() == ProcessCommandResponse(responses=[clarification_text]).model_dump()
+    # Verify save calls: user message, clarification AI response
+    assert mock_nlp_services["save_chat_message"].call_count == 2
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.USER, text=user_input)
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.AI, text=clarification_text)
+    # Ensure no action services were called
+    mock_nlp_services["delete_calendar_event"].assert_not_called()
+
+def test_process_command_error_intent(client: TestClient, db: Session, mock_nlp_services):
+    user, access_token, refresh_token = _login_user(db, client)
+    user_input = "Gibberish request"
+    error_text = "Sorry, I didn't understand that."
+    mock_nlp_services["process_request"].return_value = {
+        "intent": "error",
+        "params": {},
+        "response_text": error_text
+    }
+
+    response = client.post(
+        "/api/nlp/process-command",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"user_input": user_input}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    assert response.json() == ProcessCommandResponse(responses=[error_text]).model_dump()
+    # Verify save calls: user message, error AI response
+    assert mock_nlp_services["save_chat_message"].call_count == 2
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.USER, text=user_input)
+    mock_nlp_services["save_chat_message"].assert_any_call(db, user_id=user.id, sender=MessageSender.AI, text=error_text)
+
+# --- Tests for /history ---
+
+def test_get_history(client: TestClient, db: Session, mock_nlp_services):
+    user, access_token, refresh_token = _login_user(db, client)
+
+    # Mock the history data returned by the service
+    mock_history = [
+        ChatMessage(id=1, user_id=user.id, sender=MessageSender.USER, text="Hello", timestamp=datetime.now()),
+        ChatMessage(id=2, user_id=user.id, sender=MessageSender.AI, text="Hi there!", timestamp=datetime.now())
+    ]
+    mock_nlp_services["get_chat_history"].return_value = mock_history
+
+    response = client.get(
+        "/api/nlp/history",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    # We need to compare JSON representations as datetime objects might differ slightly
+    response_data = response.json()
+    assert len(response_data) == 2
+    assert response_data[0]["text"] == "Hello"
+    assert response_data[1]["text"] == "Hi there!"
+    mock_nlp_services["get_chat_history"].assert_called_once_with(db, user_id=user.id, limit=50)
+
+def test_get_history_unauthorized(client: TestClient):
+    response = client.get("/api/nlp/history")
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+# Add more tests for other intents (update/delete calendar/todo, unknown intent, etc.)
+# Add tests for error handling within the API endpoint (e.g., missing IDs for update/delete)
diff --git a/backend/tests/test_todo.py b/backend/tests/test_todo.py
new file mode 100644
index 0000000..573ea76
--- /dev/null
+++ b/backend/tests/test_todo.py
@@ -0,0 +1,210 @@
+import pytest
+from fastapi import status
+from fastapi.testclient import TestClient
+from sqlalchemy.orm import Session
+from datetime import date
+
+from tests.helpers import generators
+from modules.todo import schemas # Import schemas
+
+# Helper Function
+def _login_user(db: Session, client: TestClient):
+    user, password = generators.create_user(db)
+    login_rsp = generators.login(db, user.username, password)
+    return user, login_rsp["access_token"], login_rsp["refresh_token"]
+
+# --- Test CRUD Operations ---
+
+def test_create_todo(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    today_date = date.today()
+    # Format the date string to match the expected response format "YYYY-MM-DDTHH:MM:SS"
+    todo_data = {
+        "task": "Test TODO",
+        "date": f"{today_date.isoformat()}T00:00:00",
+        "remind": True
+    }
+
+    response = client.post(
+        "/api/todos/",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json=todo_data
+    )
+
+    assert response.status_code == status.HTTP_201_CREATED
+    data = response.json()
+    assert data["task"] == todo_data["task"]
+    assert data["date"] == todo_data["date"]
+    assert data["remind"] == todo_data["remind"]
+    assert data["complete"] is False # Default
+    assert "id" in data
+    assert data["owner_id"] == user.id
+
+def test_read_todos(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    # Create some todos for the user
+    client.post("/api/todos/", headers={"Authorization": f"Bearer {access_token}"}, cookies={"refresh_token": refresh_token}, json={"task": "Todo 1"})
+    client.post("/api/todos/", headers={"Authorization": f"Bearer {access_token}"}, cookies={"refresh_token": refresh_token}, json={"task": "Todo 2"})
+
+    # Create a todo for another user
+    other_user, other_password = generators.create_user(db)
+    other_login_rsp = generators.login(db, other_user.username, other_password)
+    other_access_token = other_login_rsp["access_token"]
+    other_refresh_token = other_login_rsp["refresh_token"]
+    client.post("/api/todos/", headers={"Authorization": f"Bearer {other_access_token}"}, cookies={"refresh_token": other_refresh_token}, json={"task": "Other User Todo"})
+
+
+    response = client.get(
+        "/api/todos/",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert len(data) == 2 # Should only get todos for the logged-in user
+    assert data[0]["task"] == "Todo 1"
+    assert data[1]["task"] == "Todo 2"
+
+def test_read_single_todo(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    create_response = client.post(
+        "/api/todos/",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"task": "Specific Todo"}
+    )
+    todo_id = create_response.json()["id"]
+
+    response = client.get(
+        f"/api/todos/{todo_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert data["id"] == todo_id
+    assert data["task"] == "Specific Todo"
+    assert data["owner_id"] == user.id
+
+def test_read_single_todo_not_found(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    response = client.get(
+        "/api/todos/9999", # Non-existent ID
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+def test_read_single_todo_forbidden(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+
+    # Create a todo for another user
+    other_user, other_password = generators.create_user(db)
+    other_login_rsp = generators.login(db, other_user.username, other_password)
+    other_access_token = other_login_rsp["access_token"]
+    other_refresh_token = other_login_rsp["refresh_token"]
+    other_create_response = client.post("/api/todos/", headers={"Authorization": f"Bearer {other_access_token}"}, cookies={"refresh_token": other_refresh_token}, json={"task": "Other User Todo"})
+    other_todo_id = other_create_response.json()["id"]
+
+    # Try to access the other user's todo
+    response = client.get(
+        f"/api/todos/{other_todo_id}",
+        headers={"Authorization": f"Bearer {access_token}"}, # Using the first user's token
+        cookies={"refresh_token": refresh_token}
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND # Service raises 404 if not found for *this* user
+
+def test_update_todo(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    create_response = client.post(
+        "/api/todos/",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"task": "Update Me"}
+    )
+    todo_id = create_response.json()["id"]
+
+    update_data = {"task": "Updated Task", "complete": True}
+    response = client.put(
+        f"/api/todos/{todo_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json=update_data
+    )
+
+    assert response.status_code == status.HTTP_200_OK
+    data = response.json()
+    assert data["id"] == todo_id
+    assert data["task"] == update_data["task"]
+    assert data["complete"] == update_data["complete"]
+    assert data["owner_id"] == user.id
+
+    # Verify update by reading again
+    get_response = client.get(
+        f"/api/todos/{todo_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+    assert get_response.json()["task"] == update_data["task"]
+    assert get_response.json()["complete"] == update_data["complete"]
+
+
+def test_update_todo_not_found(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    update_data = {"task": "Updated Task", "complete": True}
+    response = client.put(
+        "/api/todos/9999", # Non-existent ID
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json=update_data
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+def test_delete_todo(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    create_response = client.post(
+        "/api/todos/",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token},
+        json={"task": "Delete Me"}
+    )
+    todo_id = create_response.json()["id"]
+
+    response = client.delete(
+        f"/api/todos/{todo_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+
+    assert response.status_code == status.HTTP_200_OK # Delete returns the deleted item
+    assert response.json()["id"] == todo_id
+
+    # Verify deletion by trying to read
+    get_response = client.get(
+        f"/api/todos/{todo_id}",
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+    assert get_response.status_code == status.HTTP_404_NOT_FOUND
+
+def test_delete_todo_not_found(client: TestClient, db: Session):
+    user, access_token, refresh_token = _login_user(db, client)
+    response = client.delete(
+        "/api/todos/9999", # Non-existent ID
+        headers={"Authorization": f"Bearer {access_token}"},
+        cookies={"refresh_token": refresh_token}
+    )
+    assert response.status_code == status.HTTP_404_NOT_FOUND
+
+# --- Test Authentication/Authorization ---
+
+def test_create_todo_unauthorized(client: TestClient):
+    response = client.post("/api/todos/", json={"task": "No Auth"})
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED
+
+def test_read_todos_unauthorized(client: TestClient):
+    response = client.get("/api/todos/")
+    assert response.status_code == status.HTTP_401_UNAUTHORIZED