How do you ensure tests are fast and reliable in TDD?
Answer: Mock external dependencies. Keep tests focused and independent. Avoid I/O operations in unit tests. Run tests frequently during development.
What interviewers expect
- A clear definition tied to Testing in Unit Testing projects
- Trade-offs (performance, maintainability, security, cost)
- When you would and would not use it in production
Real-world example
In a production Unit Testing application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.
How to explain in the interview
- Define the concept in one or two sentences.
- Context — where it fits in Unit Testing architecture.
- Example — a specific project, bug, or performance win.
- Trade-off — what you gain vs what you sacrifice.
Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.