← System Design
SeniorAPIMicroservicesContract TestingCI/CD

Design a Scalable API Testing Platform

Design an API testing platform supporting functional, contract, integration and regression testing at scale.

The Problem

An organization has hundreds of APIs and microservices. Design a centralized testing platform that validates APIs continuously across development and deployment pipelines.

Requirements

  • Support REST and GraphQL APIs
  • Support functional API testing
  • Support contract testing
  • Validate authentication and authorization
  • Support multiple environments
  • Execute tests in parallel
  • Integrate with CI/CD
  • Provide centralized reporting

High-Level Architecture

Client / CI-CD Pipeline
Test Orchestrator
Execution / Platform Services
Test Workers
Application Under Test
Results + Observability

Architecture Components

Test Definition Layer — stores reusable API test scenarios.

API Client Layer — handles REST and GraphQL communication.

Authentication Layer — manages authentication strategies.

Contract Validation Layer — validates API contracts.

Execution Engine — executes tests in parallel.

Environment Configuration — manages environment-specific endpoints and settings.

Result Store — persists execution results.

Reporting Layer — provides trends and failure analysis.

CI/CD Integration — triggers tests during builds and deployments.

Senior QA Perspective

The platform should validate more than HTTP status codes. I would include schema validation, business rules, contract compatibility, authentication, authorization, negative scenarios and service dependencies. For microservices, contract testing becomes important because API consumers and providers can evolve independently.

Interviewer Follow-ups

  • How would you test APIs with dependent services?
  • How would you handle authentication tokens?
  • How would you test GraphQL?
  • How would you implement contract testing?
  • How would you manage test data?
  • Which API tests should run in a deployment pipeline?

Free Resource

Senior QA Interview Pack

50 senior QA questions, automation problems, API testing, system design scenarios and frameworks for answering at a senior level.

Free. Practical. Built for senior QA interviews.