⚡ Section 10 — Mid-Level Masterclass

Automated Testing & Test Pyramid Strategy

Stop relying on manual QA clicking. Build production-grade automated test suites with pytest, fixtures, parametrization, mocking, and coverage.

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Manual UI Click Testing vs Automated Pytest Suite

Never rely on manual form clicking. Automated test suites execute in milliseconds, block broken PRs, and allow safe refactoring.

❌ Manual QA Form Clicking (Slow & Unreliable)

# ❌ Takes 15 minutes of manual labor
# 1. Open browser
# 2. Click sign-up form
# 3. Type credentials manually
# 4. Check database manually...
# ❌ Zero coverage, zero CI integration!

✅ Automated Pytest Suite (Sub-Second Execution)

# ✅ Runs 50 tests in < 1 second via pytest
def test_create_user_api_success(client):
    res = client.post("/users", json={"email": "test@dev.com", "password": "Pass!"})
    assert res.status_code == 201
    assert res.json()["email"] == "test@dev.com"

🔺 The Test Pyramid & Directory Architecture

1. Unit Tests (tests/unit/)

➔

2. Integration Tests (tests/integration/)

➔

3. API Tests (tests/api/)

➔

4. E2E Tests (tests/e2e/)

🛠️ Pytest Essential Toolkit

@pytest.fixture

Reusable setup/teardown contexts for DB sessions and test clients.

@pytest.mark.parametrize

Executes a single test function against multiple input datasets.

unittest.mock (patch)

Mocks external HTTP requests, SMTP email clients, and payment gateways.

pytest-cov (--cov)

Measures code coverage percentage and flags untested line branches.

💻 Production Blueprint: Shared Fixtures & Parametrization

Notice how `conftest.py` sets up dependency overrides while `@pytest.mark.parametrize` verifies edge cases.

# ─── 1. SHARED TEST FIXTURES (tests/conftest.py) ──────────────────────────
import pytest
from fastapi.testclient import TestClient

@pytest.fixture
def mock_repo():
    return InMemoryUserRepository()

@pytest.fixture
def client(mock_repo):
    app.dependency_overrides[get_user_repo] = lambda: mock_repo
    with TestClient(app) as c:
        yield c

# ─── 2. PARAMETRIZED UNIT TEST (tests/unit/test_users.py) ──────────────────
@pytest.mark.parametrize("pwd, is_valid", [
    ("short", False),
    ("ValidSecret123!", True),
])
def test_password_validation(pwd: str, is_valid: bool):
    assert validate_password(pwd) == is_valid