Unit Testing Interview Questions

Use unit tests with mocks or fakes for external dependencies, integration tests against a real database or message broker when appropriate, and contract tests for APIs. Unit Testing should have clear inputs/outputs so tests remain fast and deterministic.

Log structured events with correlation IDs, track latency and error rates, and alert on SLO breaches. For Unit Testing, capture enough context to reproduce failures without logging secrets such as passwords or tokens.

Auth often gates access to endpoints or resources that rely on Unit Testing. Apply least privilege, validate tokens or sessions at the boundary, and never trust client-side checks alone. Mention OAuth, JWT, or session cookies as appropriate to the stack.

Separate config from code using environment-specific settings, secrets managers, and twelve-factor practices. Document required variables for Unit Testing so deployments to staging and production remain repeatable and auditable.

Consider idempotency, status codes, pagination, versioning, and error payloads. Unit Testing should not leak internal exceptions to clients; return consistent error shapes and document them in OpenAPI or similar specs.

Catch exceptions at appropriate layers, map them to user-safe messages, retry transient failures with backoff where suitable, and record failures for operators. Avoid swallowing errors silently—failed Unit Testing operations should be visible in logs and metrics.

Use the official .NET docs for Unit Testing, language or framework references, and reputable community guides. Bookmark release notes and migration guides when upgrading versions, since Unit Testing behavior can change between releases.

Copying snippets without understanding why Unit Testing works leads to fragile code. Beginners often skip error handling, tests, or edge cases. Slow down, trace execution step by step, and validate assumptions with small experiments.

Describe where Unit Testing runs relative to middleware, endpoints, and DI. Mention hosting (Kestrel) and how configuration binds for Unit Testing.

async/await, records, nullable reference types, and LINQ. Show how they improve correctness for Unit Testing.

xUnit + Moq/NSubstitute, WebApplicationFactory for integration, and in-memory providers when appropriate. Keep Unit Testing tests deterministic.

Singleton vs scoped vs transient depends on state and DbContext rules. Justify the lifetime for Unit Testing with a concrete example.

Options pattern, validation on start, and secrets outside source control. Document required settings for Unit Testing.

ILogger with structured properties, correlation IDs, and no secrets in logs. Map Unit Testing exceptions to problem details for APIs.

Middleware for cross-cutting pipeline concerns; filters for MVC/minimal APIs specifics. Pick the narrowest layer that fits Unit Testing.

Follow team conventions, split concerns into testable units, handle edge cases, and document assumptions. Review similar modules in the codebase, add observability, and ship incrementally with feature flags if Unit Testing is risky.

Watch for bottlenecks, shared state races, config drift, and unbounded resource usage. Load-test Unit Testing paths, set limits, and plan horizontal scaling or caching before traffic spikes.

One approach optimizes simplicity and time-to-market; the other optimizes performance, flexibility, or compliance. Choose based on team skill, traffic, and maintenance horizon—there is rarely a single best answer for Unit Testing.

Reproduce in staging, check logs/metrics/traces, narrow scope with binary search deploys, and write a postmortem. Fix Unit Testing root cause, add regression tests, and improve alerts so similar failures are caught earlier.

Check correctness, tests, naming, error handling, security, and performance. Ask whether Unit Testing belongs in this layer, if docs updated, and if rollback is safe.