"How do you approach API testing?"
APIs are the backbone of modern applications. This tests your understanding of API quality assurance beyond just checking status codes.
Cover the layers: functional, performance, security, contract testing.
Describe your tooling and automation approach.
Discuss edge cases and error handling validation.
Mention CI/CD integration and monitoring.
I test APIs across four dimensions. Functional: verify each endpoint returns correct data for valid inputs, proper error codes for invalid inputs, and handles edge cases like empty arrays and null values. Contract: ensure the API matches its OpenAPI spec and does not break consumers — I use tools like Pact for consumer-driven contract tests. Performance: load test critical endpoints to establish baselines and catch regressions. Security: test authentication, authorization, input validation, and rate limiting. I automate all of this in Postman collections or pytest suites integrated into CI. Every PR runs the full API test suite, and I monitor production API health with alerts on error rate spikes.
Go beyond happy-path testing — edge cases and error handling matter most.
Mention contract testing to show you think about API consumers.
Discuss both pre-deployment testing and production monitoring.
Postman/Newman for exploratory and automated tests, pytest/requests for code-based tests, k6 or JMeter for load testing, and Pact for contract testing. Choose based on team preference and integration needs.
Test with valid tokens, expired tokens, missing tokens, and tokens with insufficient permissions. Verify that protected endpoints reject unauthorized requests and return appropriate error codes.
Contract testing verifies that an API meets the expectations of its consumers without running a full integration test. It catches breaking changes early, especially in microservice architectures.
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