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FastAPI Blog Project - Testing Guide

This guide explains how to write and run tests for the FastAPI Blog Project.

📁 Project Test Structure

tests/
├── __init__.py          # Makes tests a Python package
├── conftest.py          # Shared fixtures and configuration
├── test_main.py         # Tests for app configuration
├── test_users.py        # Tests for user endpoints
└── test_blogs.py        # Tests for blog endpoints

🚀 Quick Start

Install Testing Dependencies

pip install pytest pytest-asyncio pytest-cov httpx

Or install all dependencies:

pip install -r requirements.txt

Run All Tests

pytest

Run Tests with Verbose Output

pytest -v

Run Specific Test File

pytest tests/test_users.py
pytest tests/test_blogs.py

Run Specific Test Class

pytest tests/test_users.py::TestCreateUser

Run Specific Test

pytest tests/test_users.py::TestCreateUser::test_create_user_success

📊 Code Coverage

Run Tests with Coverage Report

pytest --cov=app tests/

Generate HTML Coverage Report

pytest --cov=app --cov-report=html tests/

Then open htmlcov/index.html in your browser.

Generate Coverage Report with Missing Lines

pytest --cov=app --cov-report=term-missing tests/

🧪 Writing Tests

Basic Test Structure

from fastapi import status

class TestFeatureName:
    """Tests for a specific feature."""
    
    def test_something_success(self, client):
        """Test successful operation."""
        response = client.get("/api/v1.0/endpoint/")
        assert response.status_code == status.HTTP_200_OK
    
    def test_something_failure(self, client):
        """Test failure case."""
        response = client.get("/api/v1.0/nonexistent/")
        assert response.status_code == status.HTTP_404_NOT_FOUND

Using Fixtures

Fixtures provide reusable test data and setup. Available fixtures in conftest.py:

# Use the test client
def test_example(client):
    response = client.get("/api/v1.0/users/")
    assert response.status_code == 200

# Use sample data
def test_create_user(client, sample_user_data):
    response = client.post("/api/v1.0/users/", json=sample_user_data)
    assert response.status_code == 201

# Use pre-created user
def test_with_user(client, created_user):
    user_id = created_user["id"]
    response = client.get(f"/api/v1.0/users/{user_id}")
    assert response.status_code == 200

Creating Custom Fixtures

Add to conftest.py:

@pytest.fixture
def custom_data():
    """Custom test data."""
    return {
        "field1": "value1",
        "field2": "value2"
    }

@pytest.fixture
def authenticated_client(client, sample_user_data):
    """Client with authentication (if you add auth)."""
    # Create user and get token
    client.post("/api/v1.0/users/", json=sample_user_data)
    # Login and get token
    # Add token to headers
    return client

🔧 Test Configuration

pytest.ini Options

[pytest]
testpaths = tests              # Where to find tests
addopts = -v --tb=short        # Default options
markers =                       # Custom markers
    slow: marks tests as slow
    integration: integration tests

Using Markers

import pytest

@pytest.mark.slow
def test_slow_operation(client):
    """This test takes a long time."""
    pass

@pytest.mark.integration
def test_integration(client):
    """This is an integration test."""
    pass

Run tests excluding slow tests:

pytest -m "not slow"

🗄️ Database Testing

Tests use an in-memory SQLite database instead of your real database:

  • Tests won't affect your production data
  • Each test gets a fresh database
  • Tests run faster

How It Works

# conftest.py sets up a test database
SQLALCHEMY_DATABASE_URL = "sqlite:///:memory:"

# Override the database dependency
app.dependency_overrides[get_db] = override_get_db

📝 Common Test Patterns

Testing CRUD Operations

class TestResource:
    def test_create(self, client):
        response = client.post("/api/v1.0/resource/", json={"data": "value"})
        assert response.status_code == 201
    
    def test_read(self, client):
        # Create first, then read
        create_resp = client.post("/api/v1.0/resource/", json={"data": "value"})
        resource_id = create_resp.json()["id"]
        
        response = client.get(f"/api/v1.0/resource/{resource_id}")
        assert response.status_code == 200
    
    def test_update(self, client):
        # Create, then update
        create_resp = client.post("/api/v1.0/resource/", json={"data": "value"})
        resource_id = create_resp.json()["id"]
        
        response = client.put(
            f"/api/v1.0/resource/{resource_id}", 
            json={"data": "updated"}
        )
        assert response.status_code == 200
    
    def test_delete(self, client):
        # Create, then delete
        create_resp = client.post("/api/v1.0/resource/", json={"data": "value"})
        resource_id = create_resp.json()["id"]
        
        response = client.delete(f"/api/v1.0/resource/{resource_id}")
        assert response.status_code in [200, 204]

Testing Validation Errors

def test_missing_required_field(self, client):
    response = client.post("/api/v1.0/resource/", json={})
    assert response.status_code == 422  # Validation error

def test_invalid_data_type(self, client):
    response = client.post("/api/v1.0/resource/", json={"id": "not-an-int"})
    assert response.status_code == 422

Testing Error Responses

def test_not_found(self, client):
    response = client.get("/api/v1.0/resource/99999")
    assert response.status_code == 404
    assert "not found" in response.json()["detail"].lower()

🎯 Best Practices

  1. One assertion per concept - Each test should verify one thing
  2. Descriptive names - test_create_user_with_duplicate_email_fails
  3. Arrange-Act-Assert - Setup, execute, verify
  4. Use fixtures - Reuse common setup code
  5. Test edge cases - Empty inputs, invalid data, boundaries
  6. Keep tests independent - Each test should work in isolation

🔄 Continuous Integration

Add to your CI pipeline (e.g., GitHub Actions):

- name: Run tests
  run: |
    pip install -r requirements.txt
    pytest --cov=app --cov-report=xml

- name: Upload coverage
  uses: codecov/codecov-action@v3

🆘 Troubleshooting

Tests can't find modules

# Make sure you're in the project root
cd /path/to/FastAPI_Blog_Project
pytest

Database errors in tests

  • Check that SQLite is available
  • Ensure conftest.py properly overrides get_db

Async test issues

# Install pytest-asyncio
pip install pytest-asyncio

📚 Resources