🔬 SDET interview prep

// WHO THIS IS FOR

For engineers interviewing for Software Development Engineer in Test roles — where the expectation is production-quality code, framework ownership, and the ability to design test infrastructure other engineers rely on. Covers mid-to-senior scopes where interviewers assess your coding ability, design instincts, and understanding of CI/CD and test observability.

// SKILLS INTERVIEWERS EXPECT

Green = most frequently tested

// TYPICAL INTERVIEW ROUNDS

1. 1

   Coding screen

   45–60 min live coding or take-home. Expect data-structure and OOP problems at a moderate level — linked lists, hash maps, class hierarchies — as well as writing a small test utility or parser from scratch. Interviewers are grading code quality and naming, not just correctness: clean abstractions, meaningful test cases for your own code, and the ability to reason about edge cases under time pressure.

2. 2

   Framework and architecture design

   Whiteboard or discussion round: design a test framework for a given system from scratch. Cover layer separation (test / page object / data / config), your choice of runner and assertion library, how to handle fixtures and parallel execution, and the trade-offs you made. You may be asked to critique an existing framework for brittleness or scale problems. Senior roles extend to plugin architecture, custom reporters, and API abstraction layers shared across teams.

3. 3

   CI/CD and system design

   Walk through a complete pipeline: trigger on PR, run unit and integration tests in parallel, spin up a Docker test environment, run E2E suites with sharding, publish results to Allure, and gate the merge. Expect deep follow-ups on secret management, caching strategies, flaky-test detection, and rolling back a broken pipeline. Senior roles may include Kubernetes-based test infrastructure or self-hosted runner management.

4. 4

   Behavioural and engineering culture

   How you advocate for test quality in a team that treats tests as second-class code; how you handle a legacy codebase with zero tests; how you conduct code review on test PRs. Interviewers also probe how you balance framework ownership with feature delivery timelines and how you onboard other engineers onto the framework you built.

// TOPICS TO STUDY

• OOP principles applied to test code: encapsulation, inheritance, polymorphism, SOLID
• Page Object Model vs Screenplay pattern vs component-based abstraction — trade-offs
• Factory and Builder patterns for scalable test data construction
• Dependency injection in test frameworks (Spring for Java, tsyringe / inversify for TS)
• Custom assertions, matchers, and retry mechanisms
• GitHub Actions: matrix builds, layer caching, artifact upload, test result publishing
• Docker: multi-stage builds for test images, Selenium Grid with Docker Compose
• Test observability: structured logging, Allure integration, metrics dashboards
• Code review: identifying brittle selectors, hidden test coupling, and anti-patterns

// READINESS SELF-CHECK