The red-green-refactor rhythm sounds obvious until someone is watching you type and you instinctively want to write the full implementation before the test.
Start by clarifying the scope and constraints (e.g., single currency, concurrency, persistence) before diving into code. Then walk through the TDD cycle for each feature, emphasizing the red-green-refactor rhythm and how you'd evolve the design incrementally. Finally, discuss trade-offs and how you'd handle edge cases like overdrafts and transfers.
Pro tip: Demonstrate discipline by resisting the urge to over-engineer early; keep each implementation as simple as possible to pass the test, and let the design emerge through refactoring. This shows you understand that TDD is a design tool, not just a testing technique.
Ask questions to understand the expected behavior, edge cases, and non-functional requirements (e.g., concurrency, persistence, currency). This ensures you're solving the right problem and sets the stage for incremental development.
Create a minimal project structure with a test framework (e.g., pytest). Write a failing test for the first feature (open account) that defines the expected API and behavior.
Write just enough production code to make the test pass, even if it's hardcoded or naive. This validates the test and keeps momentum.
Refactor to improve design without changing behavior, then move to the next feature (deposit, withdraw, etc.). Repeat the red-green-refactor cycle, ensuring each new test drives new functionality.
After covering all features, summarize design decisions, trade-offs (e.g., simplicity vs. extensibility), and how you'd handle production concerns like concurrency, persistence, and error handling.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.