At which stages of the software development lifecycle does a testing engineer participate?

A testing engineer participates in almost all stages of the SDLC:

1. Planning: Involved in defining quality requirements, risk assessment, testing strategy, and scope planning.
2. Requirements analysis: Analyzing and clarifying requirements, identifying ambiguities and incompleteness, developing test scenarios based on requirements.
3. Design: Analyzing architecture and design, participating in designing test frameworks and test environment.
4. Development: Early testing (early involvement), participating in developing automated tests (if applicable).
5. Testing: Main activity — performing various types of testing (functional, non-functional, regression, etc.), analyzing results, registering defects, tracking fixes.
6. Deployment: Post-deployment testing, verifying operability in the production environment.
7. Maintenance: Conducting regression testing when releasing patches, updates, or new versions, analyzing user feedback.