API Testing with Postman | Complete Guide + Interview Q & A

Learn to create and send a get request with Postman, understand essential status codes, and validate the response body for real API testing.

Master get, post, put, and delete by exploring how they retrieve, create, update, and remove data in Postman. Apply crud concepts with real-world examples like user signups and product listings.

Learn to validate API responses by checking status codes, response body data, and headers in Postman. Ensure correct data and formats with a focus on common codes and body structure.

Perform a real-time API test with a free public API in Postman, validating status code 200, JSON response fields (id, name, username, email), and headers and response time.

Show that a 200 OK does not guarantee business correctness by validating technical aspects (status, response time, headers) and functional outcomes (correct data and completed actions) in API testing.

Get api should be read-only and safe; changing data violates rest principles, and modification should use post, port, or patch.

Evaluate how a 204 no content response signals a successful request with no body, for delete, put, or patch operations; validate against business requirements to decide pass or fail.

Investigate why a delete API may return success (200 or 204) while data remains, indicating a bug or mismatched state, with causes like delayed operations or soft delete not reflected.

Explain why PUT and PATCH have different purposes: PUT replaces the entire resource, while PATCH updates specified fields. Learn how misusing them can cause data loss and API design concerns.

Develop a step-by-step api troubleshooting routine: validate request details (url, endpoints, http method, headers, payload), diagnose network, server status, timeouts, and use debugging logs and Postman console.

Systematically diagnose a no-response API by validating request details (url, endpoints, http method, headers, payload), checking network, server availability, and using debugging logs to identify client, network, or server issues.

Verify the presence and validity of the authentication token, headers, and credentials to ensure the request is properly authenticated and that the token matches the correct environment (dev, QA, prod).

Investigate why get works but post fails by checking the request payload and configuration. Validate the JSON, mandatory fields, content-type, and API contract to troubleshoot post issues.

Validate the payload and headers, verify API contract, and retry with different data. Check environment and logs, reproduce the issue, isolate the cause, and report a backend defect with evidence.

Assess API response time by validating actual metrics with Postman, compare to the SLA, and retest across peak and non-peak hours while analyzing payload, parameters, environment, and backend factors.

Understand negative testing in Postman by examining how the API responds to invalid, missing, or incorrect inputs, and verify proper error codes and messages.

Learn why an API works in Postman but fails in the application by comparing request headers, authentication, payload, and environment config to identify root causes.

Organize APIs into a collection and run them sequentially with the collection runner for data-driven testing.

Learn to validate API responses with multiple records using Postman by checking structure, ensuring the array is not empty, validating field types and values, data accuracy, and edge cases.

Learn to test the same API across dev, QA, and prod with Postman by using environment variables for base URL, token, and other values, switching environments without editing requests.

Test invalid login scenarios in Postman by sending incorrect credentials, verify codes and error messages, ensure no sensitive data exposure, and confirm login is not successful with multiple failed attempts.