💡Overview

API Testing Overview

An API (Application Programming Interface) is a software intermediary that allows two applications to talk to each other. Think of APIs as the messenger that delivers requests and responses between systems in a standardized, predictable way.

APIs use defined endpoints, protocols and data formats to receive and send requests programmatically. Common request methods through endpoints include GET, POST, PUT and DELETE which map to CRUD operations of retrieving, creating, updating and deleting information. Params in the URL and body specify exactly what is being requested from the API.

Successful requests receive a 2xx status response code while 4xx/5xx denote client and server errors respectively. The response body then contains the requested data neatly formatted as JSON or XML to be easily parsed. External APIs usually require an authentication token in the headers as well for security.

Well documented APIs specify these request formats, endpoints, data structures and authentication process. This enables seamless third party integration. APIs also abstract internal implementation details and allow data exchange across platforms since code/language barriers are eliminated through agreed standards.

Why test APIs? APIs form the backbone of many applications and services. Ensuring APIs are stable, secure, and functional is critical. API testing verifies:

• Correctness - The API functions as intended and returns expected results and status codes.

• Security - The API handles authentication, authorization, and verifies input as expected.

• Performance - The API responds within defined time constraints under load.

• Compatibility - The API remains compatible with dependent systems.

What to test? Aspects of an API to test include:

• Functional testing - Test behavior and functional requirements.

• Regression testing - Make sure existing functionality still works after changes.

• Security testing - Strong authentication, authorization, input validation.

• Performance/load testing - API responds appropriately under various loads.

• Usability testing - Usability for API consumers.

• Compatibility testing - Works with different SDKs and client applications.

Tools for API testing Popular API testing tools include:

• Postman - Write and execute test collections to test APIs.

• SoapUI - Performs automated testing of web services and APIs.

• Newman - CLI tool to run Postman collections.

• Karate - DSL for testing REST and GraphQL APIs.

Benefits of API testing

• Finds bugs early before release

• Ensures stability and reliability

• Improves API design over time

• Gives confidence to API consumers

Advantages of API Testing:

• External interfaces can be tested without impacting the internal application code. This allows testing early in the development process.

• Automated API tests are faster and more reliable than manual tests, and can test at scale across different environments.

• Bugs in the API contract or implementation are caught early before they impact clients.

• Tests act as documentation by validating API expectations and behaviors.

• New/changes to APIs can be tested before client code updates to prevent breaking changes.

• Variations in input parameters, edge cases and error conditions can be thoroughly tested.

Disadvantages of API Testing:

• API implementations may change without adjusting tests, leading to false positives/negatives. Close coordination is needed.

• Setting up test infrastructure, scripts and environments requires more initial effort than testing a GUI.

• Third party services used via APIs may have rate limiting or access restrictions affecting testing scope.

• Slow/unstable network connections can impact test reliability compared to internal app testing.

• Covering all response variations and different client scenarios may be difficult to exhaustively test.

• Finding and reproducing transient, timing-dependent issues can be challenging.