Created Python Tests for the core functionalities

.github/workflows/test-backend.yml

@@ -0,0 +1,53 @@
+name: Backend Tests
+
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    services:
+      postgres:
+        image: postgres:16
+        env:
+          POSTGRES_USER: postgres
+          POSTGRES_PASSWORD: postgres
+          POSTGRES_DB: devbin_test
+        ports:
+          - 5433:5432
+        options: >-
+          --health-cmd "pg_isready -U postgres"
+          --health-interval 5s
+          --health-timeout 5s
+          --health-retries 5
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.13'
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+        with:
+          version: "latest"
+
+      - name: Install dependencies
+        run: uv sync --extra test --extra migration
+
+      - name: Run tests
+        env:
+          APP_DATABASE_URL: postgresql+asyncpg://postgres:postgres@localhost:5433/devbin_test
+          APP_BASE_FOLDER_PATH: /tmp/devbin_test_files
+          APP_DEBUG: "true"
+          APP_CORS_DOMAINS: '["http://test"]'
+          APP_ALLOW_CORS_WILDCARD: "false"
+        run: uv run pytest

README.md

@@ -140,6 +140,22 @@ APP_RELOAD=true
 APP_SQLALCHEMY_ECHO=true
 ```
 
+### Tests
+
+### Backend Tests
+
+Run tests with:
+
+```bash
+cd backend
+uv run pytest
+```
+
+> If you modified any of the core API endpoints, make sure to run the tests to ensure they still work as expected. Or if
+> you are committing breaking changes, please adjust them and add a note why this breaking change is necessary.
+
+See [Testing](/backend/TESTING.md)
+
 ### API Endpoints
 
 - `GET /health` – Health check

Taskfile.yml

@@ -11,3 +11,15 @@ tasks:
     env:
       APP_DEBUG: true
     cmd: docker compose --profile dev_backend up -d --build
+  dev:down:
+    cmds:
+      - docker compose --profile dev_frontend down
+      - docker compose --profile dev_backend down
+      - docker compose --profile dev_db down
+  dev:reset:
+    cmds:
+      - docker compose --profile dev_frontend down
+      - docker compose --profile dev_backend down --volumes
+      - docker compose --profile dev_db down --volumes
+      - docker compose --profile dev_frontend up -d --build
+      - docker compose --profile dev_backend up -d --build

backend/TESTING.md

@@ -0,0 +1,263 @@
+# Testing Guide
+
+This guide explains how to run tests locally and in CI/CD.
+
+## Quick Start
+
+### 1. Install Test Dependencies
+
+```bash
+uv sync --extra test
+```
+
+### 2. Start Test Database
+
+```bash
+# Start PostgreSQL test database in Docker
+./scripts/setup_test_db.sh
+```
+
+This will:
+
+- Start PostgreSQL 16 in Docker on port 5433
+- Create the `devbin_test` database
+- Wait for the database to be ready
+
+### 3. Run Tests
+
+```bash
+# Run all tests
+uv run pytest
+
+# Run only unit tests (no database required)
+uv run pytest tests/unit/ -v
+
+# Run with coverage report
+uv run pytest --cov=app --cov-report=html
+
+# Run in parallel (faster)
+uv run pytest -n auto
+
+# Run specific test file
+uv run pytest tests/unit/test_token_utils.py -v
+```
+
+## Test Structure
+
+```
+tests/
+├── unit/              # Fast tests, no external dependencies
+├── integration/       # Tests with database and file system
+├── api/              # Full API endpoint tests
+└── security/         # Security-focused tests
+```
+
+## Local Development
+
+### Managing Test Database
+
+```bash
+# Start test database
+docker-compose -f docker-compose.test.yml up -d
+
+# Stop test database
+docker-compose -f docker-compose.test.yml down
+
+# Clean up database and volumes
+docker-compose -f docker-compose.test.yml down -v
+
+# View logs
+docker-compose -f docker-compose.test.yml logs -f
+```
+
+### Test Database Connection
+
+- **Host**: localhost
+- **Port**: 5433 (to avoid conflicts with dev database on 5432)
+- **Database**: devbin_test
+- **User**: postgres
+- **Password**: postgres
+- **Connection String**: `postgresql://postgres:postgres@localhost:5433/devbin_test`
+
+### Environment Variables
+
+Tests use environment variables from `pytest.ini` by default:
+
+```ini
+APP_DATABASE_URL = postgresql+asyncpg://postgres:postgres@localhost:5433/devbin_test
+APP_BASE_FOLDER_PATH = /tmp/devbin_test_files
+APP_DEBUG = true
+APP_ALLOW_CORS_WILDCARD = true
+```
+
+You can override these by setting environment variables before running tests:
+
+```bash
+export APP_DATABASE_URL=postgresql+asyncpg://postgres:postgres@localhost:5432/my_test_db
+uv run pytest
+```
+
+## CI/CD Setup
+
+### GitHub Actions
+
+The test database is automatically configured in `.github/workflows/test.yml`:
+
+```yaml
+services:
+  postgres:
+    image: postgres:16
+    env:
+      POSTGRES_USER: postgres
+      POSTGRES_PASSWORD: postgres
+      POSTGRES_DB: devbin_test
+    ports:
+      - 5432:5432
+```
+
+In CI, tests use port 5432 (the default PostgreSQL port in the service container).
+
+### Running Tests in CI
+
+```bash
+# CI sets APP_DATABASE_URL to use the service container
+pytest -v --cov=app --cov-report=xml
+coverage report --fail-under=80
+```
+
+## Test Categories
+
+### Unit Tests (Fast, Isolated)
+
+```bash
+pytest tests/unit/ -m unit
+```
+
+- No database or file system
+- Mock external dependencies
+- < 1ms per test
+- Test utilities, validators, pure functions
+
+### Integration Tests
+
+```bash
+pytest tests/integration/ -m integration
+```
+
+- Real database with transaction rollback
+- File system operations (temp directories)
+- 10-100ms per test
+- Test service layer
+
+### API Tests
+
+```bash
+pytest tests/api/
+```
+
+- Full HTTP request/response cycle
+- All middleware included
+- 50-200ms per test
+- Test endpoints, rate limiting, caching
+
+## Coverage Reports
+
+### View HTML Coverage Report
+
+```bash
+uv run pytest --cov=app --cov-report=html
+open htmlcov/index.html  # or xdg-open on Linux
+```
+
+### Coverage Targets
+
+- Overall: 80%+ (enforced in CI)
+- Critical modules: 90%+
+    - `app/services/paste_service.py`
+    - `app/utils/token_utils.py`
+    - `app/api/subroutes/pastes.py`
+
+## Troubleshooting
+
+### Database Connection Errors
+
+**Problem**: `connection refused` or `could not connect to server`
+
+**Solution**:
+
+1. Check if test database is running: `docker ps | grep devbin_test`
+2. Start database: `./scripts/setup_test_db.sh`
+3. Check database logs: `docker-compose -f docker-compose.test.yml logs`
+
+### Port Already in Use
+
+**Problem**: Port 5433 is already in use
+
+**Solution**:
+
+1. Change port in `docker-compose.test.yml`
+2. Update `pytest.ini` to match
+3. Restart database
+
+### Tests Fail Randomly
+
+**Problem**: Tests pass sometimes, fail other times (flaky tests)
+
+**Solution**:
+
+1. Check if tests are properly isolated (no shared state)
+2. Verify database cleanup between tests
+3. Check for timing issues (use `freezegun` for time-based tests)
+
+### Slow Tests
+
+**Problem**: Tests take too long to run
+
+**Solution**:
+
+1. Run tests in parallel: `pytest -n auto`
+2. Run only unit tests: `pytest tests/unit/`
+3. Run specific test file instead of entire suite
+4. Check for N+1 query issues in integration tests
+
+## Best Practices
+
+### Writing New Tests
+
+1. **Use descriptive names**: `test_create_paste_with_valid_data_returns_200`
+2. **Test one thing**: Each test should verify one specific behavior
+3. **Use fixtures**: Reuse common setup via pytest fixtures
+4. **Clean up**: Tests should not leave artifacts (files, DB records)
+5. **Mark tests**: Use `@pytest.mark.unit` or `@pytest.mark.integration`
+
+### Test Data
+
+- Use `faker` for realistic test data (IPs, user agents, names)
+- Use `sample_paste_data` fixture for consistent paste creation
+- Create factory functions for complex test objects
+
+### Mocking
+
+- **Mock external services**: Time, disk usage checks, network calls
+- **Use real implementations**: Database, file system (with temp dirs)
+- **Mock sparingly**: Real implementations catch more bugs
+
+## Continuous Integration
+
+Tests run automatically on:
+
+- Push to `master` or `develop`
+- Pull requests
+
+### CI Requirements
+
+- All tests must pass
+- Coverage must not decrease
+- Coverage must be >= 80%
+- Linting must pass (ruff)
+
+### Viewing CI Results
+
+1. Go to GitHub Actions tab
+2. Click on the latest workflow run
+3. View test results and coverage report

backend/Taskfile.yml

@@ -3,11 +3,17 @@
 version: '3'
 
 tasks:
+  api:setup_test:
+    cmds:
+      - uv sync --extra test
+      - ./scripts/setup_test_db.sh
   api:start:
     env:
       APP_DEBUG: true
     cmd: uv run main.py
   api:migrate:
     cmd: alembic upgrade head
   api:downmigrate:
-    cmd: alembic downgrade -1
+    cmd: alembic downgrade -1
+  api:test:
+    cmd: uv run pytest

backend/alembic/env.py

@@ -1,10 +1,9 @@
 import os
 from logging.config import fileConfig
 
+from alembic import context
 from sqlalchemy import engine_from_config, pool
 
-from alembic import context
-from app.db.base import Base
 from app.db.models import *
 
 # this is the Alembic Config object, which provides