pytest-test-data-factory-pattern

A Python QA Automation lab demonstrating how the Factory Pattern simplifies test data generation for API, RBAC, and multi-tenant scenarios.

Built with FastAPI, pytest, factory_boy, SQLAlchemy, and SQLite.

Why this project exists

Test suites become hard to maintain when data is created manually inside each test. This project shows a cleaner approach: factories centralize object creation, fixtures prepare isolated execution environments, and tests stay focused on behavior rather than setup.

Technologies

Area	Technology
Language	Python
API framework	FastAPI
Testing framework	pytest
Test data generation	factory_boy
Fake data	Faker
ORM	SQLAlchemy
Database	SQLite (in-memory for tests)
API client for tests	FastAPI TestClient / httpx2
Test reports	pytest-html

Setup

python -m venv .venv

# Windows
.venv\Scripts\activate

# macOS/Linux
source .venv/bin/activate

pip install -r requirements.txt

Commands

# Run tests (generates report.html)
pytest -v

# Run the API locally
uvicorn app.main:app --reload

Project structure

├── app/
│   ├── database.py       # SQLAlchemy engine, session, get_db dependency
│   ├── models.py         # Tenant, Role, User, Project, EPD
│   ├── schemas.py        # Pydantic request/response schemas
│   └── main.py           # FastAPI app and endpoints
├── tests/
│   ├── conftest.py       # db_session, client, admin_user, viewer_user fixtures
│   ├── factories.py      # factory_boy factories for all domain entities
│   ├── helpers.py        # auth_headers() utility
│   ├── test_health.py
│   ├── test_projects.py  # RBAC and tenant isolation tests
│   ├── test_epds.py      # EPD edge case tests
│   └── test_factories.py # Factory behavior tests
├── requirements.txt
└── pytest.ini

Domain model

A small multi-tenant SaaS platform with four core entities:

Tenant
├── Users  (role: admin | viewer)
├── Projects
└── EPDs   (Environmental Product Declaration, with a gwp float field)

Key design concepts

Factory Pattern

Factories live in tests/factories.py and centralize object creation. Tests declare what they need without repeating setup logic:

tenant = TenantFactory()
admin = AdminUserFactory(tenant=tenant)
project = ProjectFactory(tenant=tenant)
outlier_epd = EPDFactory(tenant=tenant, gwp=999999)

Relationships are resolved automatically via SubFactory. Overrides are explicit and local to the test that needs them.

pytest fixtures

Fixtures in conftest.py prepare the execution environment:

• db_session — in-memory SQLite, created and dropped per test
• client — FastAPI TestClient with the DB dependency overridden
• admin_user / viewer_user — pre-committed users ready for use

Factories generate entities. Fixtures prepare the context in which tests run.

Test isolation

Each test gets a fresh in-memory SQLite database. No shared state, no cleanup scripts, no ordering dependencies.

Authentication

Authentication is intentionally simple: tests pass a user ID via the X-User-Id header, resolved against the test database. The focus is on test data generation and authorization logic, not auth infrastructure.

Multi-tenant isolation

Tenant boundaries are enforced at the query level. Every list endpoint filters by the authenticated user's tenant_id. Direct access by ID to another tenant's resource returns 404.

RBAC

Two roles: admin and viewer. Mutation endpoints (POST /projects, DELETE /projects/{id}, POST /epds) require the admin role and return 403 otherwise.

API endpoints

GET  /health
GET  /projects
GET  /projects/{project_id}
POST /projects
DELETE /projects/{project_id}
GET  /epds
POST /epds

Test coverage

File	What it covers
test_health.py	/health returns 200
test_projects.py	Admin can create/delete, viewer blocked, tenant isolation
test_epds.py	Valid EPD, negative gwp rejected, outliers, duplicates, incomplete payload
test_factories.py	Relationships auto-generated, overrides work