Application Programming Interface (API) testing has become increasingly important as more applications are built using a microservices architecture. Thorough API testing ensures the APIs used by the front and back end systems communicate and share data properly. There are several ways developers and testers can gain API testing skills.
Learn API Testing Basics
New API testers should start by learning the basics of API testing. Some key topics include:
- What is an API?
- Common API protocols like REST and SOAP
- API testing concepts like functional testing, load testing, security testing, etc.
- How to write test cases for APIs
- Tools used for API testing like Postman and Swagger
Taking an online course or reading introductory books/articles on API testing will build a solid foundation to start practicing hands-on API testing.
Explore Sample APIs
One of the best ways to learn API testing is to actually test some APIs. Many public APIs are available which allow developers to test API calls. Some good sample APIs to try include:
- OpenWeatherMap – Provides weather data for any location
- Twitter API – Allow accessing and tweaking Twitter accounts
- Reddit API – Programmatically access Reddit data
- YouTube API – Add/manage videos, playlists, channels and more
- Google Maps API – Integrate Google Maps into applications
Start making API calls to these sample APIs using Postman or your language/framework of choice. Try out different requests like GET, POST, PUT and DELETE. See how the API responds with different parameters. This will build familiarity with real-world APIs.
Set Up a Practice API Server
To gain complete control over the environment, set up a simple API server on your local machine. Frameworks like Express (Node.js) and Flask (Python) make it easy to spin up a barebones API. You can create custom endpoints that return test data in JSON/XML format. The advantages of a local server include:
- No usage limits like public APIs
- Consistent, predictable responses
- Endpoints tailored to learning goals
- Can intentionally introduce bugs/errors
As your API testing skills improve, level up the complexity of your practice API server by adding new endpoints, request parameters, HTTP codes and authentication.
Write a Complete API Testing Plan
With a practice API available, put together a formal testing plan that would be applied for a real-world API. The plan should include:
- Functional test cases – Inputs, endpoints, expected responses
- Test data/datasets to use in requests
- Validation criteria for responses
- Test coverage for positive and negative scenarios
- Automation ideas for regression testing
Treating your practice API as a real product will help develop skills like analyzing requirements, identifying edge cases and writing effective test cases.
Perform Security Testing
Security testing is an crucial part of API testing. Some techniques to try:
- Fuzz testing – Send malformed/random data to endpoints
- Authentication/authorization testing – Try accessing endpoints with invalid or missing credentials
- Injection attacks – Attempt SQL injection, cross-site scripting, etc. on input fields
- Rate limiting – Verify API handles excessive requests properly
- Penetration testing – Use tools like OWASP ZAP to find vulnerabilities
Improving skills in identifying and mitigating API vulnerabilities will help you test the security of any real-world API.
Perform Load and Performance Testing
How an API performs under heavy load is critical. Try load testing your practice API using tools like Artillery, Locust or JMeter. Some scenarios to test include:
- Gradually increasing traffic volume to find max capacity
- Spiking traffic to mimic sudden surges
- Sustaining heavy load for extended periods
- Testing with globally distributed load generators
- Identifying performance bottlenecks
This will develop skills in benchmarking, load modeling and analyzing API performance.
Integrate API Testing in CI/CD
For real projects, API testing should be automated and run as part of continuous integration/deployment pipelines. With your practice API, explore:
- Writing automated API test cases using libraries like SuperTest (NodeJS) or Requests (Python)
- Executing API tests with every code change using CI tools like Jenkins, CircleCI or TravisCI
- Running API contract tests to validate compatibility with consumers
- Shifting left by testing API endpoints as they’re developed
This will help put API testing skills into actual practice within a devops environment.
Learn From Existing API Test Code
Reading well-written API test code is a great way to improve skills. Studying open source projects can reveal patterns like:
- Organizing tests with descriptors like unit, integration, functional, etc.
- Setting up test fixtures and templates
- Making effective assertions
- Mocking external services dependencies
- Validating responses against schemas
Contribute to open source API testing code to get feedback from senior developers.
Attend API Testing Conferences/Workshops
Conferences like API World and API Strategy bring together testing practitioners discussing the latest in the field. Look for talks, workshops and training covering:
- New API testing tools and best practices
- Automation techniques
- Security and performance testing
- Test design for APIs
- Monitoring and analytics
Attending in-person or online will accelerate learning by connecting with experts around API testing.
Get API Testing Certifications
Getting certified can validate and improve API testing skills. Some popular certifications include:
- ISTQB Certified Tester – API Testing
- Postman API Testing Certification
- Tricentis API Testing Certification
- Parasoft SOA Certified Professional
Certifications measure skills through exams and performance-based testing. They can boost credibility and job prospects for API testers.
Stay Up-to-Date via Blogs/Newsletters
Follow leading API testing blogs, newsletters and experts to learn about new tools, evolving best practices and testing innovations including:
- The Quantum API Newsletter
- Nordic APIs Blog
- API Testing Blog by Inflectra
- Joe Colantonio Test Automation Blog
- Alan Richardson Blog
Actively staying up-to-date will ensure your API testing skills always reflect current industry approaches.
Conclusion
With API testing becoming essential for modern software applications, developers and testers should look to actively build skills in this area. Hands-on practice against sample APIs, creating a practice server, learning from open source projects and connecting with experts will accelerate learning. Organizations should also invest in API testing training and certification to strengthen their testing practices.