API Testing Interview Questions 2026

Describe JSON Schema Validation and its importance in API testing. What is a JSON schema? How do you validate that an API response conforms to the expected schema using Rest Assured or Postman? Give an example schema for a user object with required fields and type constraints.

Explain the difference between PUT and PATCH in REST APIs. When is each appropriate? Show how you would test both verbs using Playwright's APIRequestContext, and explain how to validate partial vs full resource updates.

Explain common HTTP status codes returned by APIs (2xx, 3xx, 4xx, 5xx). Differentiate between 401 vs 403, 404 vs 400, and 502 vs 503. How do you validate these in automated API tests?

Differentiate between Path Parameters and Query Parameters in REST APIs. Give examples: /users/{id} vs /users?role=admin. When should each be used? How do you pass and validate them in automated API tests using Rest Assured or Postman?

How do you test a REST API that requires OAuth 2.0 authentication? Walk through obtaining a token (client credentials flow), storing it, using it in subsequent requests, and handling token expiry in your automation framework.

How can nested JSON responses be handled in API testing? Show how to extract a deeply nested value (e.g., response.data.user.address.city) using Rest Assured's JsonPath, and how to validate arrays of objects within the response.

How would you test a payments API endpoint for race conditions where two simultaneous requests might both succeed at deducting from the same account balance?

In Postman, how would you chain two requests so the second one uses an ID returned by the first, without hardcoding it?

What's the difference between testing a REST API's status code and testing its response schema? Why do you need both?

How would you test that a "cancel ride" API endpoint correctly refunds a rider only when the cancellation happens within the free-cancellation window, and charges a fee otherwise?