Create Unit Tests for the Controller and Interceptor

Implement unit tests for other NestJS components

A NestJS application contains many components. In this lesson, we’ll discuss unit testing for different NestJS components. We’ll delve into implementing unit tests for a controller and an interceptor with hands-on examples.

What components should be unit tested in NestJS?

When writing unit tests for a NestJS application, it’s generally advisable to focus on testing components that contain business logic or significantly impact the application’s functionality.

Below is the list of components that should be tested, as well as those that might not require unit tests.

Components to test

• Controllers: They handle incoming requests, and it’s crucial to test them to verify if they respond correctly to different scenarios, handle validation, and interact appropriately with services.

• Services: They contain the application’s business logic and are often the heart of the NestJS application. Testing service methods, including edge cases and error handling, is essential to validate their behavior.

• Interceptors: They can modify the request/response globally. Testing ensures they work as intended and don’t introduce unintended side effects.

• Guards: They control access to routes based on certain conditions. Testing guards ensure they correctly enforce authorization rules.

• Pipes: They transform incoming data before reaching the controller. Testing ensures they correctly modify the data according to their specifications.

Components that might not require unit tests

• DTOs: They are simple data structures used for data transfer and typically don’t contain business logic.

• Entities: They represent database models often generated or managed by ORMs. Testing entities might be covered in integration tests that involve interactions with the database.

• Module files: In NestJS, they mainly handle the configuration and assembly of the application. Testing module files are typically covered by end-to-end testing rather than unit testing.

Create unit tests for UserController

Controllers in NestJS handle incoming requests and orchestrate the data flow within the application. Testing a controller involves creating mock services to isolate controller tests and ensure the controller produces the expected response.

We have UserController that includes the CRUD endpoints.