This was the core question and it took a while to realize they wanted me to think about ALL the edge cases systematically, not just write a few happy-path tests.
Start by clarifying the maze representation, controller API, and test objectives, then systematically design tests for each edge case, grouping them by category (e.g., pathfinding, state management, performance). Prioritize tests that validate correctness and robustness, and discuss how you would structure the suite for maintainability and fast feedback.
Pro tip: Emphasize test isolation and determinism: use dependency injection for the maze and cheese placement, and avoid relying on timing or randomness. This makes tests reliable and fast, which is crucial for continuous integration.
Ask about the maze data structure, controller methods, expected behaviors, and constraints (e.g., time limits, memory). Confirm what 'unreachable cheese' means and how errors are reported.
Group the given edge cases into logical categories: trivial mazes (single-cell), pathfinding challenges (unreachable, narrow corridors, cul-de-sacs, loops), state management (repeated visits, backtracking), multi-goal (multiple cheeses), and non-functional (performance, API errors).
For each category, outline specific test scenarios: e.g., for single-cell, test with and without cheese; for unreachable, assert no path and proper error; for narrow corridors, verify correct path; for loops, ensure no infinite loops; for repeated visits, check visit counts; for backtracking, verify path reversal; for multiple cheeses, test optimal order; for performance, set timeouts; for API errors, test invalid inputs.
Propose a test framework (e.g., JUnit, pytest) and structure: unit tests for controller logic, integration tests for maze solving. Use mocks for maze and cheese to isolate the controller. Include setup/teardown for consistent state.
Explain how you balance thoroughness with test execution speed, and how you ensure coverage of all edge cases. Mention metrics like code coverage and mutation testing to validate test quality.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by defining a minimal interface for the maze that your code depends on, then create a test double (stub or fake) that implements this interface with predetermined, deterministic behavior. Use dependency injection to swap the real maze implementation with your test double in unit tests, ensuring tests are fast, repeatable, and isolated from external factors.
Pro tip: Emphasize that deterministic tests should avoid randomness and time-based dependencies; use fixed seeds or precomputed paths, and consider using a mocking framework to reduce boilerplate while keeping tests readable.
Determine the methods and properties your code uses from the maze (e.g., getCell, isWall, getStart, getEnd). Define a clear interface if one doesn't exist.
Decide between a stub (returns canned answers) or a fake (simplified implementation). For deterministic tests, a stub with fixed responses is often sufficient.
Create a class or object that implements the maze interface, with methods returning hardcoded values or values from a predefined data structure (e.g., a 2D array).
Use dependency injection (constructor, setter, or parameter) to replace the real maze with your test double in the unit test setup.
Write tests that assert expected behavior using the test double, ensuring no reliance on randomness, external state, or timing.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the definition of 'first cheese'—whether it's based on search order (e.g., BFS/DFS) or spatial proximity. Then outline a testing strategy that includes unit tests with controlled mazes, assertions on the returned cheese's coordinates, and edge cases like multiple cheeses at equal distances. Emphasize deterministic behavior and reproducibility.
Pro tip: Mention that you would test with a maze where the 'first' cheese is not the closest to the start, to ensure the controller follows the correct traversal order rather than a heuristic. This shows you understand the difference between algorithmic order and intuitive proximity.
Ask the interviewer to define 'first cheese'—is it the first encountered in a BFS, DFS, or other traversal? This determines the expected output.
Create small, hand-crafted mazes with multiple cheeses placed at known positions relative to the start and each other, ensuring the traversal order is unambiguous.
For each maze, assert that the controller returns the cheese at the expected coordinates, and verify it does not return any other cheese.
Test scenarios like multiple cheeses at the same distance, cheeses in different branches, and mazes where the first cheese is not the closest to the start.
Generate random mazes and compare the controller's output against a reference implementation of the traversal algorithm to ensure correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the controller's expected behavior and the maze representation, then design a test that constructs a maze with a known cycle and asserts termination within a bounded number of steps. Use a timeout or step counter to detect infinite loops, and verify the controller either finds a valid path or correctly reports no path.
Pro tip: Mention that you'd also test edge cases like self-loops and multiple cycles, and use a deterministic maze to make the test reproducible. This shows you think about robustness and test reliability.
Ask or state assumptions about the maze structure (e.g., grid, graph), the controller's interface, and what 'handles cycles' means (e.g., avoids infinite loops, finds path if exists).
Create a simple maze that contains at least one cycle, such as a 2x2 open grid or a graph with a back edge, ensuring the cycle is reachable from the start.
Specify that the controller should terminate within a reasonable time or step limit, and either return a valid path or indicate no path exists.
Write a test that runs the controller on the cyclic maze, using a timeout or a maximum iteration count to fail if the controller does not terminate.
Assert the controller's output is correct, and consider additional tests for self-loops, multiple cycles, and unreachable goals to ensure comprehensive coverage.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.