Edge Cases and Complex Testing Questions

Covers identification and systematic handling of edge cases and strategies for testing difficult or non deterministic scenarios. Topics include enumerating boundary conditions and pathological inputs, designing test cases for empty, single element, maximum and invalid inputs, and thinking through examples mentally before and after implementation. Also covers complex testing scenarios such as asynchronous operations, timing and race conditions, animations and UI transients, network dependent features, payment and real time flows, third party integrations, distributed systems, and approaches for mocking or simulating hard to reproduce dependencies. Emphasis is on pragmatic test design, testability trade offs, and strategies for validating correctness under challenging conditions.

EasyTechnical

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List strategies to reliably unit-test asynchronous functions (e.g., JavaScript Promises or Python async/await). Cover deterministic scheduling, timeouts, synthetic clocks, awaiting promises, and avoiding false positives from tests that complete before async work finishes.

EasyTechnical

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Describe how you would test UI transients such as spinners, toast messages, or temporary modals in an automated test suite. What do you assert deterministically, what can be flaky, and what should be covered by manual testing or visual inspection?

MediumSystem Design

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Design unit, integration, and E2E tests for a feature that loads content from a CDN and retries on 5xx/timeout errors with exponential backoff. Describe how you would simulate CDN timeouts, partial content, cache staleness, and verify correct retry/backoff behavior without causing slow tests.

HardTechnical

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Explain methods to make tests for nondeterministic distributed algorithms (leader election, consensus) reproducible. Discuss deterministic scheduling, model checking, inserting controlled randomness, failure injection, and the trade-offs between simulation fidelity and test determinism.

HardTechnical

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You maintain a complex canvas-based animation (e.g., collaborative whiteboard) that must render consistently across browsers and variable frame rates. Propose approaches to automate visual regression tests for animations, including frame sampling strategies, pixel-tolerance thresholds, hashing approaches, and tools/frameworks you would evaluate.

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