# Unit Testing (Node.js / NestJS)

> Jest, test suites, mocking, spies, test coverage, testing providers, controllers

- 20 interview questions
- Junior
- [Interview Questions: Node.js / NestJS](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions.md)

## 1. What is the role of the describe() function in Jest?

**Answer**

The describe() function groups multiple related tests together in a test suite. It improves readability by organizing tests by feature or component. Each describe() can contain multiple it() or test() to describe individual behaviors.

## 2. What is the difference between it() and test() in Jest?

**Answer**

There is no functional difference between it() and test() in Jest. They are two aliases that do exactly the same thing. The choice between them is purely a matter of style and writing preference. Some prefer it() for a more natural BDD syntax, others prefer test() for clarity.

## 3. Which Jest matcher should be used to verify that a value is strictly equal to another?

**Answer**

The toBe() matcher checks strict equality using the === operator in JavaScript. It compares references for objects, meaning two objects with the same content but different references won't be equal. To compare object content, use toEqual() instead.

## 17 more questions available

- What is the difference between toEqual() and toStrictEqual()?
- How to execute code before each test in a Jest suite?

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## Other Node.js / NestJS interview topics

- [Node.js Fundamentals](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/nodejs-fundamentals.md): 20 questions, Junior
- [Node.js Core APIs](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/nodejs-core-apis.md): 25 questions, Junior
- [Asynchronous Programming](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/asynchronous-programming.md): 25 questions, Junior
- [Express.js Basics](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/express-basics.md): 20 questions, Junior
- [NestJS Fundamentals](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/nestjs-fundamentals.md): 23 questions, Junior
- [REST API Design](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/rest-api-design.md): 20 questions, Junior
- [Validation & DTO](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/validation-dto.md): 20 questions, Junior
- [API Documentation & Contracts](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/api-documentation.md): 20 questions, Junior
- [Error Handling](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/error-handling.md): 20 questions, Junior
- [Task Scheduling](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/scheduling-cron.md): 15 questions, Junior
- [NestJS Modules & DI](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/nestjs-modules-di.md): 20 questions, Mid-Level
- [Configuration & Environment Management](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/configuration-environment.md): 20 questions, Mid-Level
- [JWT Authentication](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/authentication-jwt.md): 25 questions, Mid-Level
- [Authorization & RBAC](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/authorization-rbac.md): 20 questions, Mid-Level
- [Database with TypeORM](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/database-typeorm.md): 30 questions, Mid-Level
- [Prisma ORM](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/prisma-orm.md): 25 questions, Mid-Level
- [Middleware & Interceptors](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/middleware-interceptors.md): 20 questions, Mid-Level
- [File Upload](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/file-upload.md): 15 questions, Mid-Level
- [WebSockets](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/websockets.md): 20 questions, Mid-Level
- [GraphQL with NestJS](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/graphql-basics.md): 25 questions, Mid-Level
- [End-to-End Testing](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/testing-e2e.md): 20 questions, Mid-Level
- [Caching with Redis](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/caching-redis.md): 20 questions, Mid-Level
- [Queues with Bull](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/queues-bull.md): 20 questions, Mid-Level
- [DevOps, Logging & CI/CD](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/logging-monitoring.md): 25 questions, Mid-Level
- [Docker & Containerization](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/docker-containerization.md): 25 questions, Mid-Level
- [Microservices](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/microservices.md): 30 questions, Senior
- [Security Best Practices](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/security-best-practices.md): 25 questions, Senior
- [Performance & Cloud Deployment](https://sharpskill.dev/en/technologies/node-nestjs/interview-questions/performance-optimization.md): 30 questions, Senior

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