API Testing Introduction

 🧪 What is API Testing?

API Testing is the process of verifying whether APIs work as expected — focusing on functionality, reliability, performance, and security.

Unlike UI testing, it doesn’t involve a browser or frontend.
Instead, you directly send requests (GET, POST, PUT, DELETE) and validate responses (status codes, response time, and data).

Key checks during API testing:

• ✅ Is the response status code correct? (e.g., 200, 404, 401)

• ✅ Is the response time within the limit?

• ✅ Are all fields and data types correct?

• ✅ Is authentication/authorization working properly?

• ✅ Are error messages meaningful?

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⚙️ How to Perform API Testing?

You can perform API Testing using manual tools or automation frameworks.

🔹 Manual API Testing

Tools like Postman, Swagger, or Insomnia help testers send requests and analyze responses without writing code.

Basic flow:

1. Launch Postman

2. Create a new request

3. Enter the API endpoint (URL)

4. Select the method (GET/POST/PUT/DELETE)

5. Add headers or authentication if needed

6. Click Send

7. Validate the response body, status code, and time

🔹 Automated API Testing

Automation tools like:

• RestAssured (Java)

• Requests + Pytest (Python)

• Karate DSL

• Postman + Newman

These help run regression suites, integrate with CI/CD (Jenkins, GitHub Actions), and generate reports automatically.

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🔍 Types of APIs

Type	Description	Example
Open APIs (Public APIs)	Available to everyone; used by third parties.	Google Maps, OpenWeather API
Internal APIs (Private APIs)	Used only within an organization for internal systems.	HRMS ↔ Payroll System
Partner APIs	Shared between specific business partners; require access tokens.	Travel site ↔ Airline partner
Composite APIs	Combine multiple endpoints in one call.	Fetch order + shipping + payment info in one response

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📘 Quick Recap

✅ API = Communication Bridge between two systems
✅ API Testing = Validating request & response
✅ Can be done manually (Postman) or automated (RestAssured, Python, etc.)
✅ Focus on status codes, response data, time, and security
✅ APIs can be Public, Private, Partner, or Composite

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🧠 Pro Tip

Start practicing with free APIs like:
🔹 https://reqres.in
🔹 https://jsonplaceholder.typicode.com
🔹 https://dummyjson.com
These are perfect for learning GET, POST, PUT, DELETE methods.