Merge pull request #2 from katariina-jarvenmaki/refactoring_and_migrations

Refactoring and migrations

.env

@@ -1 +0,0 @@
-BASE_URL=http://localhost:8000

.gitignore

@@ -1,3 +1,6 @@
 app/__pycache__
+__pycache__
+.pytest_cache/
 venv/
-test.txt
+test.txt
+diff.txt

README.md

@@ -10,7 +10,7 @@ source venv/bin/activate
 
 ## Run locally
 ```bash
-uvicorn app.main:app --reload
+python -m uvicorn app.main:app --reload --host 0.0.0.0 --port 8000
 ```
 Then check:<br> 
 http://127.0.0.1:8000<br>
@@ -23,5 +23,11 @@ http://127.0.0.1:8000/shorten
 ```bash
 PYTHONPATH=./ pytest
 export PYTHONPATH=$(pwd)
-pytest
- ```
+python -m pytest --cov=app --cov-report=term-missing
+```
+
+## Running Alembic revision
+```bash
+cd /opt/kjc/int/URL-shortener
+alembic revision --autogenerate -m "create urls table"
+```

alembic.ini

@@ -0,0 +1,118 @@
+# A generic, single database configuration.
+
+[alembic]
+# path to migration scripts
+# Use forward slashes (/) also on windows to provide an os agnostic path
+script_location = alembic
+
+# template used to generate migration file names; The default value is %%(rev)s_%%(slug)s
+# Uncomment the line below if you want the files to be prepended with date and time
+# see https://alembic.sqlalchemy.org/en/latest/tutorial.html#editing-the-ini-file
+# for all available tokens
+# file_template = %%(year)d_%%(month).2d_%%(day).2d_%%(hour).2d%%(minute).2d-%%(rev)s_%%(slug)s
+
+# sys.path path, will be prepended to sys.path if present.
+# defaults to the current working directory.
+prepend_sys_path = .
+
+# timezone to use when rendering the date within the migration file
+# as well as the filename.
+# If specified, requires the python>=3.9 or backports.zoneinfo library and tzdata library.
+# Any required deps can installed by adding `alembic[tz]` to the pip requirements
+# string value is passed to ZoneInfo()
+# leave blank for localtime
+# timezone =
+
+# max length of characters to apply to the "slug" field
+# truncate_slug_length = 40
+
+# set to 'true' to run the environment during
+# the 'revision' command, regardless of autogenerate
+# revision_environment = false
+
+# set to 'true' to allow .pyc and .pyo files without
+# a source .py file to be detected as revisions in the
+# versions/ directory
+# sourceless = false
+
+# version location specification; This defaults
+# to alembic/versions.  When using multiple version
+# directories, initial revisions must be specified with --version-path.
+# The path separator used here should be the separator specified by "version_path_separator" below.
+# version_locations = %(here)s/bar:%(here)s/bat:alembic/versions
+
+# version path separator; As mentioned above, this is the character used to split
+# version_locations. The default within new alembic.ini files is "os", which uses os.pathsep.
+# If this key is omitted entirely, it falls back to the legacy behavior of splitting on spaces and/or commas.
+# Valid values for version_path_separator are:
+#
+# version_path_separator = :
+# version_path_separator = ;
+# version_path_separator = space
+# version_path_separator = newline
+#
+# Use os.pathsep. Default configuration used for new projects.
+version_path_separator = os
+
+# set to 'true' to search source files recursively
+# in each "version_locations" directory
+# new in Alembic version 1.10
+# recursive_version_locations = false
+
+# the output encoding used when revision files
+# are written from script.py.mako
+# output_encoding = utf-8
+
+sqlalchemy.url = sqlite:///./test.db
+
+[post_write_hooks]
+# post_write_hooks defines scripts or Python functions that are run
+# on newly generated revision scripts.  See the documentation for further
+# detail and examples
+
+# format using "black" - use the console_scripts runner, against the "black" entrypoint
+# hooks = black
+# black.type = console_scripts
+# black.entrypoint = black
+# black.options = -l 79 REVISION_SCRIPT_FILENAME
+
+# lint with attempts to fix using "ruff" - use the exec runner, execute a binary
+# hooks = ruff
+# ruff.type = exec
+# ruff.executable = %(here)s/.venv/bin/ruff
+# ruff.options = --fix REVISION_SCRIPT_FILENAME
+
+# Logging configuration
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S

alembic/README

@@ -0,0 +1 @@
+Generic single-database configuration.

alembic/env.py

@@ -0,0 +1,82 @@
+from alembic import context
+from sqlalchemy import engine_from_config, pool
+from logging.config import fileConfig
+
+from app.db.base import Base
+from app.db import models
+from app.core.config import settings
+
+target_metadata = Base.metadata
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+# add your model's MetaData object here
+# for 'autogenerate' support
+# from myapp import mymodel
+# target_metadata = mymodel.Base.metadata
+target_metadata = Base.metadata
+
+# other values from the config, defined by the needs of env.py,
+# can be acquired:
+# my_important_option = config.get_main_option("my_important_option")
+# ... etc.
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+
+    config.set_main_option("sqlalchemy.url", settings.database_url)
+    context.configure(
+        url=url,
+        target_metadata=target_metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def run_migrations_online() -> None:
+    """Run migrations in 'online' mode.
+
+    In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+    connectable = engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        poolclass=pool.NullPool,
+    )
+
+    with connectable.connect() as connection:
+        context.configure(
+            connection=connection, target_metadata=target_metadata
+        )
+
+        with context.begin_transaction():
+            context.run_migrations()
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online()

alembic/script.py.mako

@@ -0,0 +1,26 @@
+"""${message}
+
+Revision ID: ${up_revision}
+Revises: ${down_revision | comma,n}
+Create Date: ${create_date}
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+${imports if imports else ""}
+
+# revision identifiers, used by Alembic.
+revision: str = ${repr(up_revision)}
+down_revision: Union[str, None] = ${repr(down_revision)}
+branch_labels: Union[str, Sequence[str], None] = ${repr(branch_labels)}
+depends_on: Union[str, Sequence[str], None] = ${repr(depends_on)}
+
+
+def upgrade() -> None:
+    ${upgrades if upgrades else "pass"}
+
+
+def downgrade() -> None:
+    ${downgrades if downgrades else "pass"}

alembic/versions/0132ba841ec5_create_urls_table.py

@@ -0,0 +1,30 @@
+"""create urls table
+
+Revision ID: 0132ba841ec5
+Revises: 
+Create Date: 2026-03-02 09:13:50.764599
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision: str = '0132ba841ec5'
+down_revision: Union[str, None] = None
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    pass
+    # ### end Alembic commands ###
+
+
+def downgrade() -> None:
+    # ### commands auto generated by Alembic - please adjust! ###
+    pass
+    # ### end Alembic commands ###

app/api/routes.py

@@ -0,0 +1,70 @@
+# app/api/routes.py
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi.responses import RedirectResponse
+from sqlalchemy.orm import Session
+
+from app.db.session import get_db
+from app.schemas.url import (
+    URLCreate,
+    URLResponse,
+    URLStatsResponse,
+    MessageResponse,
+)
+from app.services import url_service
+
+
+router = APIRouter()
+
+
+@router.get("/", response_model=MessageResponse)
+def home():
+    return {"message": "URL Shortener API"}
+
+
+@router.post("/shorten", response_model=URLResponse)
+def shorten_url(
+    request: URLCreate,
+    db: Session = Depends(get_db),
+):
+    short_url = url_service.create_short_url(db, str(request.url))
+    return {"short_url": short_url}
+
+
+@router.get("/{short_code}")
+def redirect_to_url(
+    short_code: str,
+    db: Session = Depends(get_db),
+):
+    original_url = url_service.get_original_url(db, short_code)
+
+    if not original_url:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="Shortened URL not found",
+        )
+
+    url_service.increment_clicks(db, short_code)
+
+    return RedirectResponse(url=original_url)
+
+
+@router.get("/stats/{short_code}", response_model=URLStatsResponse)
+def get_url_stats(
+    short_code: str,
+    db: Session = Depends(get_db),
+):
+    stats = url_service.get_stats(db, short_code)
+
+    if not stats:
+        raise HTTPException(
+            status_code=status.HTTP_404_NOT_FOUND,
+            detail="URL stats not found",
+        )
+
+    return stats
+
+
+@router.get("/health", response_model=MessageResponse)
+def health_check():
+    return {"message": "healthy"}

app/core/config.py

@@ -0,0 +1,38 @@
+# app/core/config.py
+
+from functools import lru_cache
+from pydantic_settings import BaseSettings
+from typing import List
+
+
+class Settings(BaseSettings):
+    app_name: str = "URL Shortener"
+    allowed_hosts: List[str] = ["*"]
+    database_url: str
+
+    # Server settings
+    host: str = "0.0.0.0"
+    port: int = 8000
+    base_url: str = "http://localhost:8000"
+
+    # Debug flag
+    debug: bool = True
+    
+    # Optional future extensions
+    rate_limit_per_minute: int = 60
+
+    class Config:
+        env_file = ".env"
+        env_file_encoding = "utf-8"
+        case_sensitive = False
+        extra = "ignore"
+
+
+# Cached singleton-style access
+@lru_cache()
+def get_settings() -> Settings:
+    return Settings()
+
+
+# Global settings instance
+settings = get_settings()

app/db/base.py

@@ -0,0 +1,6 @@
+# app/db/base.py
+
+from sqlalchemy.orm import DeclarativeBase
+
+class Base(DeclarativeBase):
+    pass

app/db/models.py

@@ -0,0 +1,57 @@
+# app/db/models.py
+
+from sqlalchemy import String, Integer, DateTime, func, Index
+from sqlalchemy.orm import Mapped, mapped_column
+from datetime import datetime
+from app.db.base import Base
+from typing import Optional
+
+class URL(Base):
+    __tablename__ = "urls"
+
+    id: Mapped[int] = mapped_column(
+        Integer,
+        primary_key=True,
+        index=True
+    )
+
+    short_code: Mapped[str] = mapped_column(
+        String(10),
+        unique=True,
+        nullable=False,
+        index=True
+    )
+
+    original_url: Mapped[str] = mapped_column(
+        String(2048),
+        nullable=False,
+        index=True
+    )
+
+    clicks: Mapped[int] = mapped_column(
+        Integer,
+        default=0,
+        nullable=False
+    )
+
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True),
+        server_default=func.now(),
+        nullable=False
+    )
+
+    last_accessed: Mapped[Optional[datetime]] = mapped_column(
+        DateTime(timezone=True),
+        nullable=True
+    )
+
+    # Additional compound index for faster lookups
+    __table_args__ = (
+        Index("idx_short_original", "short_code", "original_url"),
+    )
+
+    def __repr__(self) -> str:
+        return (
+            f"<URL(id={self.id}, short_code='{self.short_code}', "
+            f"original_url='{self.original_url}', clicks={self.clicks})>"
+        )

app/db/session.py

@@ -0,0 +1,26 @@
+# app/db/session.py
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from app.core.config import settings
+
+# Create SQLAlchemy engine
+engine = create_engine(
+    settings.database_url,
+    pool_pre_ping=True,  # helps prevent stale connections
+)
+
+# Session factory
+SessionLocal = sessionmaker(
+    autocommit=False,
+    autoflush=False,
+    bind=engine,
+)
+
+# Dependency for FastAPI
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()

app/main.py

@@ -1,124 +1,28 @@
-from fastapi import FastAPI, HTTPException
-from fastapi.responses import RedirectResponse
+# app/main.py
+
+from fastapi import FastAPI
 from contextlib import asynccontextmanager
-from app.utils import generate_short_code
-from pydantic import BaseModel, HttpUrl
-from pydantic_settings import BaseSettings
-import sqlite3
-import logging
+from app.core.config import settings
+from app.db.session import engine
+from app.db.base import Base
+from app.api.routes import router
 
-class AppSettings(BaseSettings):
-    base_url: str = "http://localhost:8000"
-    database_url: str = "urls.db"
 
-settings = AppSettings()  # Load environment variables
-
-# Set up logging configuration
-logging.basicConfig(level=logging.INFO,
-                    format="%(asctime)s - %(levelname)s - %(message)s")
-logger = logging.getLogger(__name__)
-
-# Database connection setup
 @asynccontextmanager
 async def lifespan(app: FastAPI):
-    conn = sqlite3.connect(settings.database_url)
-    conn.execute("""
-    CREATE TABLE IF NOT EXISTS urls (
-        id INTEGER PRIMARY KEY,
-        short_code TEXT UNIQUE,
-        original_url TEXT NOT NULL,
-        clicks INTEGER DEFAULT 0
-    );
-    """)
-    conn.execute("""
-    CREATE INDEX IF NOT EXISTS idx_short_code ON urls(short_code);
-    """)
-    conn.commit()
-    logger.info("Database initialized or already exists.")
+
+    Base.metadata.create_all(bind=engine)
     yield
-    conn.close()
-    logger.info("Database connection closed.")
 
-app = FastAPI(lifespan=lifespan)
-
-def get_db_connection():
-    return sqlite3.connect(settings.database_url, check_same_thread=False)
-
-class URLRequest(BaseModel):
-    url: HttpUrl
-
-@app.get("/")
-def home():
-    logger.info("Home endpoint accessed.")
-    return {"message": "URL Shortener API"}
-
-@app.post("/shorten")
-def shorten_url(request: URLRequest):
-    conn = get_db_connection()
-
-    existing = conn.execute(
-        "SELECT short_code FROM urls WHERE original_url = ?",
-        (str(request.url),)
-    ).fetchone()
-
-    if existing:
-        conn.close()
-        return {"short_url": f"{settings.base_url}/{existing[0]}"}
-
-    short_code = generate_short_code()
-    while conn.execute(
-        "SELECT 1 FROM urls WHERE short_code = ?",
-        (short_code,)
-    ).fetchone():
-        short_code = generate_short_code()
-
-    conn.execute(
-        "INSERT INTO urls (short_code, original_url, clicks) VALUES (?, ?, 0)",
-        (short_code, str(request.url))
+def create_app() -> FastAPI:
+    app = FastAPI(
+        title=settings.app_name,
+        debug=settings.debug,
     )
-    conn.commit()
-    conn.close()
 
-    return {"short_url": f"{settings.base_url}/{short_code}"}
+    app.include_router(router)
 
-@app.get("/{short_code}")
-def redirect_to_url(short_code: str):
-    conn = get_db_connection()
-    url_data = conn.execute(
-        "SELECT original_url FROM urls WHERE short_code = ?",
-        (short_code,)
-    ).fetchone()
+    return app
 
-    if url_data is None:
-        conn.close()
-        raise HTTPException(status_code=404, detail="Shortened URL not found")
-
-    original_url = url_data[0]
-
-    conn.execute(
-        "UPDATE urls SET clicks = clicks + 1 WHERE short_code = ?",
-        (short_code,)
-    )
-    conn.commit()
-    conn.close()
-
-    return RedirectResponse(url=original_url)
-
-@app.get("/stats/{short_code}")
-def get_url_stats(short_code: str):
-    logger.info(f"Stats request received for short_code: {short_code}")
-    conn = get_db_connection()
-    url_data = conn.execute("SELECT original_url, clicks FROM urls WHERE short_code = ?", (short_code,)).fetchone()
-    
-    if url_data is None: 
-        logger.warning(f"Stats not found for {short_code}.")
-        conn.close()
-        raise HTTPException(status_code=404, detail="URL stats not found")
-        
-    original_url, clicks = url_data
-    
-    conn.close()
-    
-    logger.info(f"Returning stats for {original_url}. Total clicks: {clicks}")
-    
-    return {"original_url": original_url, "clicks": clicks}
+app = create_app()
+app.router.lifespan_context = lifespan

app/schemas/url.py

@@ -0,0 +1,24 @@
+# app/schemas/url.py
+
+from pydantic import BaseModel, HttpUrl
+from datetime import datetime
+from typing import Optional
+
+
+class URLCreate(BaseModel):
+    url: HttpUrl
+
+
+class URLResponse(BaseModel):
+    short_url: str
+
+
+class URLStatsResponse(BaseModel):
+    original_url: HttpUrl
+    clicks: int
+    created_at: datetime
+    last_accessed: Optional[datetime] = None
+
+
+class MessageResponse(BaseModel):
+    message: str

app/services/url_service.py

@@ -0,0 +1,103 @@
+# app/services/url_service.py
+
+from sqlalchemy.orm import Session
+from sqlalchemy import select
+from datetime import datetime
+from typing import Optional
+
+from app.db.models import URL
+from app.utils.short_code import generate_short_code
+from app.core.config import settings
+
+SHORT_CODE_LENGTH = 6
+MAX_GENERATION_ATTEMPTS = 5
+
+
+def create_short_url(db: Session, original_url: str) -> str:
+    """
+    Create a shortened URL or return existing one if already present.
+    """
+
+    # 1️⃣ Check if URL already exists
+    existing = db.execute(
+        select(URL).where(URL.original_url == original_url)
+    ).scalar_one_or_none()
+
+    if existing:
+        return f"{settings.base_url}/{existing.short_code}"
+
+    # 2️⃣ Generate unique short code with collision handling
+    for _ in range(MAX_GENERATION_ATTEMPTS):
+        short_code = generate_short_code(SHORT_CODE_LENGTH)
+
+        collision = db.execute(
+            select(URL).where(URL.short_code == short_code)
+        ).scalar_one_or_none()
+
+        if not collision:
+            new_url = URL(
+                short_code=short_code,
+                original_url=original_url,
+            )
+            db.add(new_url)
+            db.commit()
+            db.refresh(new_url)
+
+            return f"{settings.base_url}/{new_url.short_code}"
+
+    # If we somehow fail multiple times
+    raise RuntimeError("Failed to generate unique short code")
+
+
+def get_original_url(db: Session, short_code: str) -> Optional[str]:
+    """
+    Retrieve original URL for redirection.
+    """
+
+    url_entry = db.execute(
+        select(URL).where(URL.short_code == short_code)
+    ).scalar_one_or_none()
+
+    if not url_entry:
+        return None
+
+    return url_entry.original_url
+
+
+def increment_clicks(db: Session, short_code: str) -> bool:
+    """
+    Increment click counter and update last_accessed timestamp.
+    """
+
+    url_entry = db.execute(
+        select(URL).where(URL.short_code == short_code)
+    ).scalar_one_or_none()
+
+    if not url_entry:
+        return False
+
+    url_entry.clicks += 1
+    url_entry.last_accessed = datetime.utcnow()
+
+    db.commit()
+    return True
+
+
+def get_stats(db: Session, short_code: str) -> Optional[dict]:
+    """
+    Return URL statistics.
+    """
+
+    url_entry = db.execute(
+        select(URL).where(URL.short_code == short_code)
+    ).scalar_one_or_none()
+
+    if not url_entry:
+        return None
+
+    return {
+        "original_url": url_entry.original_url,
+        "clicks": url_entry.clicks,
+        "created_at": url_entry.created_at,
+        "last_accessed": url_entry.last_accessed,
+    }

app/settings.py

@@ -1,7 +0,0 @@
-# app/settings.py
-
-import os
-
-# Example configuration
-database_url = os.getenv("DATABASE_URL", "sqlite:///default.db")
-debug = os.getenv("DEBUG", "True") == "True"

app/test_main.py

@@ -1,66 +0,0 @@
-from fastapi.testclient import TestClient
-import sys
-import os
-
-sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
-from app.main import app
-from app import settings
-import tempfile
-import pytest
-
-@pytest.fixture
-def test_client():
-    with tempfile.NamedTemporaryFile() as tmp:
-        settings.database_url = tmp.name
-        with TestClient(app) as c:
-            yield c
-
-@pytest.fixture
-def use_temp_db():
-    with tempfile.NamedTemporaryFile() as tmp:
-        settings.database_url = tmp.name
-        yield
-
-def test_home(test_client):
-    response = test_client.get("/")
-    assert response.status_code == 200
-    assert response.json() == {"message": "URL Shortener API"}
-
-def test_shorten_url(test_client):
-    response = test_client.post("/shorten", json={"url": "https://google.com"})
-    assert response.status_code == 200
-    data = response.json()
-    assert "short_url" in data
-    short_url = data["short_url"]
-    assert short_url.startswith("http://localhost:8000/")
-
-def test_redirect(test_client):
-    response = test_client.post("/shorten", json={"url": "https://google.com"})
-    short_url = response.json()["short_url"]
-    code = short_url.split("/")[-1]
-
-    redirect = test_client.get(f"/{code}", follow_redirects=False)
-    assert redirect.status_code == 307
-
-def test_duplicate_url_returns_same_code(test_client):
-    r1 = test_client.post("/shorten", json={"url": "https://example.com"})
-    r2 = test_client.post("/shorten", json={"url": "https://example.com"})
-
-    assert r1.status_code == 200
-    assert r2.status_code == 200
-    assert r1.json()["short_url"] == r2.json()["short_url"]
-
-def test_stats_endpoint(test_client):
-    response = test_client.post("/shorten", json={"url": "https://stats-test.com"})
-    code = response.json()["short_url"].split("/")[-1]
-
-    test_client.get(f"/{code}", follow_redirects=False)
-
-    stats = test_client.get(f"/stats/{code}")
-    assert stats.status_code == 200
-    data = stats.json()
-    assert data["clicks"] == 1
-
-def test_redirect_404(test_client):
-    response = test_client.get("/nonexistent", follow_redirects=False)
-    assert response.status_code == 404

app/tests/conftest.py

@@ -0,0 +1,64 @@
+# app/tests/conftest.py
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from fastapi.testclient import TestClient
+
+from app.main import app
+from app.db.base import Base
+from app.db.session import get_db
+
+
+# Use in-memory SQLite for tests
+TEST_DATABASE_URL = "sqlite+pysqlite:///:memory:"
+
+
+@pytest.fixture(scope="function")
+def db_session():
+    """
+    Creates a new database session for a test.
+    Rolls back everything after test finishes.
+    """
+
+    engine = create_engine(
+        TEST_DATABASE_URL,
+        connect_args={"check_same_thread": False},
+    )
+
+    TestingSessionLocal = sessionmaker(
+        autocommit=False,
+        autoflush=False,
+        bind=engine,
+    )
+
+    # Create tables
+    Base.metadata.create_all(bind=engine)
+
+    db = TestingSessionLocal()
+
+    try:
+        yield db
+    finally:
+        db.close()
+        Base.metadata.drop_all(bind=engine)
+
+
+@pytest.fixture(scope="function")
+def client(db_session):
+    """
+    Overrides get_db dependency to use test database.
+    """
+
+    def override_get_db():
+        try:
+            yield db_session
+        finally:
+            pass
+
+    app.dependency_overrides[get_db] = override_get_db
+
+    with TestClient(app) as c:
+        yield c
+
+    app.dependency_overrides.clear()

app/tests/test_routes.py

@@ -0,0 +1,93 @@
+# app/tests/test_routes.py
+
+import pytest
+
+
+def test_home(client):
+    response = client.get("/")
+    assert response.status_code == 200
+    assert response.json() == {"message": "URL Shortener API"}
+
+
+def test_health(client):
+    response = client.get("/health")
+    assert response.status_code == 200
+    assert response.json() == {"message": "healthy"}
+
+
+def test_shorten_url(client):
+    response = client.post(
+        "/shorten",
+        json={"url": "https://google.com"},
+    )
+
+    assert response.status_code == 200
+    data = response.json()
+
+    assert "short_url" in data
+    assert data["short_url"].startswith("http://")
+
+
+def test_shorten_invalid_url(client):
+    response = client.post(
+        "/shorten",
+        json={"url": "not-a-valid-url"},
+    )
+
+    assert response.status_code == 422  # Pydantic validation error
+
+
+def test_duplicate_url_returns_same_code(client):
+    r1 = client.post("/shorten", json={"url": "https://example.com"})
+    r2 = client.post("/shorten", json={"url": "https://example.com"})
+
+    assert r1.status_code == 200
+    assert r2.status_code == 200
+
+    assert r1.json()["short_url"] == r2.json()["short_url"]
+
+
+def test_redirect_success(client):
+    shorten = client.post(
+        "/shorten",
+        json={"url": "https://redirect-test.com"},
+    )
+
+    short_url = shorten.json()["short_url"]
+    code = short_url.split("/")[-1]
+
+    response = client.get(f"/{code}", follow_redirects=False)
+
+    assert response.status_code in (302, 307)
+
+
+def test_redirect_404(client):
+    response = client.get("/nonexistent", follow_redirects=False)
+    assert response.status_code == 404
+
+
+def test_stats_success(client):
+    shorten = client.post(
+        "/shorten",
+        json={"url": "https://stats-test.com"},
+    )
+
+    short_url = shorten.json()["short_url"]
+    code = short_url.split("/")[-1]
+
+    # Trigger one click
+    client.get(f"/{code}", follow_redirects=False)
+
+    stats = client.get(f"/stats/{code}")
+
+    assert stats.status_code == 200
+    data = stats.json()
+
+    assert data["original_url"] == "https://stats-test.com"
+    assert data["clicks"] == 1
+    assert "created_at" in data
+
+
+def test_stats_404(client):
+    response = client.get("/stats/doesnotexist")
+    assert response.status_code == 404

app/utils.py

@@ -1,3 +1,5 @@
+# app/utils.py
+
 import string
 import random
 

app/utils/short_code.py

@@ -0,0 +1,8 @@
+# app/utils/short_code.py
+import string
+import random
+
+def generate_short_code(length: int = 6) -> str:
+    """Generate a random alphanumeric short code."""
+    chars = string.ascii_letters + string.digits
+    return ''.join(random.choices(chars, k=length))