Welcome to this comprehensive guide on testing custom decorators with validation pipes in Nest.js! In this article, we’ll dive into the world of decorators, pipes, and testing to ensure that your Nest.js application is robust and reliable.
What are Decorators and Validation Pipes?
Before we dive into testing, let’s quickly cover the basics. Decorators and validation pipes are essential concepts in Nest.js.
Decorators
In Nest.js, decorators are functions that can modify or extend the behavior of a class, method, or property. They are denoted by the `@` symbol followed by the decorator name. Decorators are used to add metadata to a class or method, which can then be used by the framework to perform specific actions.
@MyDecorator()
export class MyClass {
// class implementation
}
Validation Pipes
Validation pipes are a type of pipe in Nest.js that are used to validate input data. They are typically used to validate request bodies, query parameters, or route parameters. Validation pipes can be used to ensure that the input data meets specific criteria, such as formatting or value constraints.
@Post()
async createUser(
@Body(new ValidationPipe()) body: CreateUserDto,
) {
// implementation
}
Why Test Custom Decorators with Validation Pipes?
Testing custom decorators with validation pipes is crucial to ensure that your Nest.js application behaves as expected. Here are a few reasons why testing is essential:
- Ensures correctness: Testing custom decorators with validation pipes ensures that they work correctly and as expected.
- Catches errors: Testing helps catch errors and bugs early on, reducing the risk of errors propagating to production.
- Improves code quality: Testing custom decorators with validation pipes improves the overall quality of your code, making it more maintainable and reliable.
Step-by-Step Guide to Testing Custom Decorators with Validation Pipes
Now that we’ve covered the basics, let’s dive into the step-by-step guide on testing custom decorators with validation pipes.
Step 1: Create a Custom Decorator
Create a new file in your Nest.js project and define a custom decorator. For this example, let’s create a decorator that checks if a user is authenticated.
// authenticated.decorator.ts
import { Injectable } from '@nestjs/common';
import { createMetadataGetter } from '@nestjs/common/utils CREATE_METADATA_GETTER';
@Injectable()
export function Authenticated(): (target: any, propertyKey: string, descriptor: PropertyDescriptor) => void {
return (target: any, propertyKey: string, descriptor: PropertyDescriptor) => {
const originalMethod = descriptor.value;
descriptor.value = function (...args: any[]) {
if (!this.authService.checkAuth()) {
throw new UnauthorizedException();
}
return originalMethod.apply(this, args);
};
return descriptor;
};
}
Step 2: Create a Validation Pipe
Create a new file in your Nest.js project and define a validation pipe. For this example, let’s create a pipe that validates a user registration request.
// user-registration.validation-pipe.ts
import { PipeTransform, Injectable, ArgumentMetadata } from '@nestjs/common';
import { validate } from 'class-validator';
@@Injectable()
export class UserRegistrationValidationPipe implements PipeTransform {
async transform(value: any, metadata: ArgumentMetadata) {
const createUserDto = plainToClass(CreateUserDto, value);
const errors = await validate(createUserDto);
if (errors.length > 0) {
throw new BadRequestException('Invalid request');
}
return createUserDto;
}
}
Step 3: Create a Test Suite
Create a new file in your Nest.js project and define a test suite using Jest. For this example, let’s create a test suite for our custom decorator and validation pipe.
// authenticated.decorator.spec.ts
import { Authenticated } from './authenticated.decorator';
import { UserRegistrationValidationPipe } from './user-registration.validation-pipe';
import { CreateUserDto } from './create-user.dto';
describe('Authenticated Decorator and UserRegistrationValidationPipe', () => {
// define test cases
});
Step 4: Write Test Cases
Write test cases for your custom decorator and validation pipe. For this example, let’s write test cases to cover the following scenarios:
- Successful authentication with valid request data
- Failed authentication with invalid request data
- Failed authentication with unauthorized access
describe('Authenticated Decorator and UserRegistrationValidationPipe', () => {
const authService = {
checkAuth: jest.fn(() => true),
};
const createUserDto = {
username: 'username',
email: 'email@example.com',
password: 'password',
};
it('should allow authenticated users with valid request data', async () => {
const pipe = new UserRegistrationValidationPipe();
const decoratedMethod = Authenticated()(createUserDto);
const result = await decoratedMethod();
expect(result).toBe(createUserDto);
});
it('should reject unauthenticated users with invalid request data', async () => {
const pipe = new UserRegistrationValidationPipe();
const invalidCreateUserDto = {
username: '',
email: 'invalid-email',
password: '',
};
const decoratedMethod = Authenticated()(invalidCreateUserDto);
expect(decoratedMethod).rejects.toThrowError(BadRequestException);
});
it('should reject unauthenticated users with unauthorized access', async () => {
authService.checkAuth.mockReturnValue(false);
const pipe = new UserRegistrationValidationPipe();
const decoratedMethod = Authenticated()(createUserDto);
expect(decoratedMethod).rejects.toThrowError(UnauthorizedException);
});
});
Step 5: Run Your Tests
Finally, run your tests using Jest. Make sure to update your `jest.config.js` file to include the necessary configurations.
// jest.config.js
module.exports = {
preset: 'jest-preset-angular',
transform: {
'^.+\\.(ts|js|mjs)$': 'ts-jest',
},
moduleNameMapper: {
'^@/(.*)$': '/src/$1',
},
};
Conclusion
In this article, we covered the importance of testing custom decorators with validation pipes in Nest.js. We walked through a step-by-step guide on creating a custom decorator and validation pipe, as well as writing test cases to cover various scenarios.
By following this guide, you can ensure that your custom decorators and validation pipes are working correctly and as expected, which will improve the overall quality and reliability of your Nest.js application.
Additional Resources
For more information on testing in Nest.js, I recommend checking out the following resources:
- Nest.js official documentation on testing: https://docs.nestjs.com/testing
- Jest official documentation: https://jestjs.io/docs/en/getting-started
- Class-validator official documentation: https://github.com/typestack/class-validator
Testing custom decorators with validation pipes is an essential part of ensuring the correctness and reliability of your Nest.js application. By following this guide, you’ll be well on your way to writing robust and maintainable code.
Frequently Asked Question
Nest.js is an amazing framework for building server-side applications, but testing custom decorators with validation pipes can be a bit tricky. Here are some FAQs to help you navigate this challenge!
Q: How do I create a test for a custom decorator in Nest.js?
A: To test a custom decorator, you can create a new instance of the decorator and pass in the necessary arguments. Then, use a mocking library like Jest or Moq to mock out any dependencies. For example, if your decorator takes a `ValidationPipe` as an argument, you can mock it using `jest.mock` and then test that the decorator behaves as expected.
Q: How do I test a custom validator within a validation pipe in Nest.js?
A: To test a custom validator, you can create a test instance of the `ValidationPipe` and pass in the custom validator as an argument. Then, use a testing library like Jest to create a test object with valid and invalid data, and assert that the validator returns the expected results. For example, you can use `expect(validationPipe.transform(validData)).toEqual(validData)` to test that the validator returns the valid data unchanged.
Q: How do I mock out dependencies in a custom decorator for testing?
A: To mock out dependencies in a custom decorator, you can use a mocking library like Jest to create mock instances of the dependencies. For example, if your decorator takes a `Logger` instance as an argument, you can create a mock logger using `jest.mock` and then pass it to the decorator. You can then assertions to verify that the decorator behaves as expected.
Q: Can I use a testing framework like Jest to test my custom decorator?
A: Yes! Jest is a popular testing framework that comes bundled with Nest.js. You can use it to write unit tests for your custom decorator, including tests for the validation pipe. Jest provides a lot of useful features out of the box, including mocking, spying, and assertions, which can make testing your custom decorator a breeze.
Q: How do I ensure that my custom decorator is properly integrated with the Nest.js framework?
A: To ensure that your custom decorator is properly integrated with the Nest.js framework, you can create an end-to-end test that exercises the decorator in the context of a Nest.js application. This can involve creating a test module that imports your decorator and uses it to decorate a controller or service. You can then use a testing library like Jest to write assertions that verify that the decorator behaves as expected.
