In Jest UT, Nest can't resolve dependencies
  • 10-May-2023
Lightrun Team
Author Lightrun Team
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In Jest UT, Nest can't resolve dependencies

In Jest UT, Nest can’t resolve dependencies of the RedisService (?). Please make sure that the argument Symbol(REDIS_CLIENT) at index [0] is available in the RootTestModule context.

Lightrun Team
Lightrun Team
10-May-2023

Explanation of the problem

During the development of a Nest.js application, a user encountered an error when running unit tests that involved the usage of Jest and the nestjs-redis module for Redis operations. Despite attempting to mock the dependencies using fn(), the user continued to face the same issue. The error message received indicated that Nest.js was unable to resolve the dependencies of the RedisService. Specifically, it mentioned that the argument Symbol(REDIS_CLIENT) at index [0] needed to be available in the RootTestModule context. The error message also provided potential solutions to address the problem, such as checking if Symbol(REDIS_CLIENT) was a provider and if it was part of the current RootTestModule, or ensuring that the module exporting Symbol(REDIS_CLIENT) was imported within the RootTestModule.

import { Test, TestingModule } from '@nestjs/testing';
import { CatsController } from './cats.controller';
import { CatsService } from './cats.service';
import { getModelToken } from '@nestjs/mongoose';
import { RedisService } from '../../shared/lib/redis/redis.service';

describe('CatsController', () => {
  let controller: CatsController;
  let service: CatsService;

  beforeEach(async () => {
    const app: TestingModule = await Test.createTestingModule({
      controllers: [CatsController],
      providers: [
        CatsService,
        RedisService,
        { provide: getModelToken('Cats'), useValue: { Symbol: jest.fn() } },
      ],
    }).compile();

    controller = app.get<CatsController>(CatsController);
    service = app.get<CatsService>(CatsService);
  });

  // ...
});

Within the unit test suite, a specific scenario called “Cats List” was being tested. The test case aimed to ensure that the findAll method of the CatsController returned the correct response. To achieve this, the getAll method of the CatsService was spied on using jest.spyOn to mock its behavior. In one test case, the getAll method was mocked to resolve with a successful response, containing an array of cat data. The expected outcome was to receive the same response from the controller.findAll() method. In another test case, the getAll method was mocked to reject with an error message indicating that no records were found. The expectation was to catch the error and verify that the error message matched the expected value.

describe('Cats List', () => {
  it('should return all cats', async () => {
    jest.spyOn(service, 'getAll').mockResolvedValue({ data: catsData, success: true });
    const catsList = await controller.findAll();
    expect(catsList).toEqual({ data: catsData, success: true });
  });

  it('should throw error record not found', async () => {
    jest.spyOn(service, 'getAll').mockRejectedValue({ message: 'Records not found' });
    try {
      await controller.findAll();
    } catch (e) {
      expect(e.message).toBe('Records not found');
    }
  });
});

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Problem solution for In Jest UT, Nest can’t resolve dependencies of the RedisService (?). Please make sure that the argument Symbol(REDIS_CLIENT) at index [0] is available in the RootTestModule context.

To address the issue of Nest.js being unable to resolve the dependencies of the RedisService while running unit tests, several modifications were made to the test setup. First, the beforeEach hook was replaced with beforeAll to ensure that the setup code is executed only once before all the test cases. The providers in the TestingModule configuration were overridden with mock values to prevent the connection to a real Redis instance. The RedisService was explicitly overridden with a mock implementation, where the get and getClient methods were mocked using jest.fn(). Additionally, the REDIS_CLIENT constant, representing the Redis client, was provided with a mock value that included mocked implementations for the get and keys methods. These changes ensured that the Redis dependencies were properly resolved and the tests could proceed without encountering the dependency resolution error.

describe('CatsController', () => {
  let controller: CatsController;
  let service: CatsService;

  beforeAll(async () => {
    const app: TestingModule = await Test.createTestingModule({
      imports: [],
      controllers: [CatsController],
      providers: [
        CatsService,
        { provide: getModelToken('Cats'), useValue: { Symbol: jest.fn() } },
        {
          provide: RedisService,
          useValue: {
            get: jest.fn(),
            getClient: jest.fn().mockReturnValue(REDIS_CLIENT),
          },
        },
        {
          provide: REDIS_CLIENT,
          useValue: {
            get: jest.fn().mockReturnValue('foo'),
            keys: jest.fn().mockReturnValue(['foo', 'bar']),
          },
        },
      ],
    }).compile();

    controller = app.get<CatsController>(CatsController);
    service = app.get<CatsService>(CatsService);
  });

  // ...
});

Other popular problems with nestjs-redis

Problem: Inability to establish a connection to server

One common issue encountered when using nestjs-redis is the inability to establish a connection with the Redis server. This problem can manifest as connection timeouts, authentication failures, or other connection-related errors. The root cause of this issue can vary, including misconfigured connection settings, network connectivity problems, or incorrect authentication credentials.

Solution:

To address this problem, it is necessary to review and verify the Redis server configuration, including the host, port, password, and any additional connection options. Additionally, checking the network connectivity between the application server and the Redis server is crucial. It is recommended to test the connection using a Redis client outside of the Nest.js application to ensure that the Redis server is accessible.

 

Problem: Data serialization and deserialization

Another common issue with nestjs-redis is related to data serialization and deserialization when interacting with Redis. Redis stores data as strings, so when working with complex data types, such as objects or arrays, it is necessary to serialize the data into a string representation before storing it in Redis and deserialize it back into its original form when retrieving it. Failure to properly handle data serialization can lead to data corruption or unexpected behavior.

Solution:

The solution is to use a serialization library, such as JSON or MessagePack, to serialize and deserialize the data.

Problem: Handling Redis transactions

A common challenge with nestjs-redis is handling Redis transactions. Redis transactions allow you to group multiple commands and execute them atomically. However, due to the nature of Redis being single-threaded, using transactions might not provide the expected atomicity in certain scenarios. This can lead to unexpected results and inconsistencies in data.

Solution:

To address this issue, it is essential to understand the limitations of Redis transactions and consider alternative approaches, such as using Lua scripts or optimistic locking mechanisms. Here’s an example of using a Lua script to ensure atomicity:

import { Injectable } from '@nestjs/common';
import { RedisService } from 'nestjs-redis';

@Injectable()
export class MyService {
  constructor(private readonly redisService: RedisService) {}

  async incrementCounter(key: string): Promise<number> {
    const script = `
      local counter = redis.call('GET', KEYS[1])
      if not counter then
        counter = 0
      end
      counter = counter + 1
      redis.call('SET', KEYS[1], counter)
      return counter
    `;
    const result = await this.redisService.getClient().eval(script, 1, key);
    return Number(result);
  }
}

A brief introduction to nestjs-redis

Nestjs-redis is a powerful module that enables seamless integration of Redis, an in-memory data store, with Nest.js applications. It provides a convenient and expressive way to interact with Redis, leveraging the benefits of Redis’s high-performance data storage and caching capabilities. This module simplifies the process of working with Redis by offering a set of decorators, providers, and utilities that streamline the integration process.

At its core, nestjs-redis utilizes the official Redis client for Node.js, providing a reliable and efficient interface to communicate with Redis servers. It offers support for various Redis features, including key-value storage, pub-sub messaging, transactions, and more. With nestjs-redis, developers can easily configure and manage Redis connections, handle data serialization and deserialization, and utilize advanced Redis functionality within their Nest.js applications.

To get started with nestjs-redis, you can install the module via npm and configure it within your Nest.js application. By defining the necessary providers and decorators, you can inject Redis clients into your services and controllers, allowing seamless interaction with Redis data. This module also offers flexibility in terms of configuration options, enabling customization of Redis connection parameters, such as the host, port, password, and database index. With nestjs-redis, you can harness the power of Redis to optimize data storage, caching, and real-time data processing in your Nest.js applications, enhancing performance and scalability.

Most popular use cases for nestjs-redis

  1. Caching: nestjs-redis provides robust caching capabilities for Nest.js applications. By leveraging Redis’s in-memory storage, developers can implement efficient caching mechanisms to store frequently accessed data, such as query results, API responses, or computed values. This helps reduce the load on databases or external APIs, improving overall application performance. Here’s an example of how to use caching with nestjs-redis:
import { CACHE_MANAGER, Inject } from '@nestjs/common';
import { Cache } from 'cache-manager';

@Injectable()
export class MyService {
  constructor(@Inject(CACHE_MANAGER) private cacheManager: Cache) {}

  async getData(key: string): Promise<any> {
    const cachedData = await this.cacheManager.get(key);
    if (cachedData) {
      return cachedData;
    }

    const data = await this.fetchDataFromDatabase();

    // Cache the data for future use
    await this.cacheManager.set(key, data, { ttl: 60 });

    return data;
  }
}
  1. Session Management: nestjs-redis can be utilized for session management in Nest.js applications. By storing session data in Redis, it becomes easier to handle session-based authentication, user sessions, and session persistence across multiple instances or servers. This ensures a scalable and distributed session management solution. Here’s an example of how to use nestjs-redis for session management:
import { Injectable } from '@nestjs/common';
import { RedisService } from 'nestjs-redis';

@Injectable()
export class SessionService {
  constructor(private readonly redisService: RedisService) {}

  async createSession(sessionId: string, userData: any): Promise<void> {
    const redisClient = this.redisService.getClient();
    await redisClient.set(sessionId, JSON.stringify(userData));
  }

  async getSession(sessionId: string): Promise<any | null> {
    const redisClient = this.redisService.getClient();
    const sessionData = await redisClient.get(sessionId);
    return sessionData ? JSON.parse(sessionData) : null;
  }

  async deleteSession(sessionId: string): Promise<void> {
    const redisClient = this.redisService.getClient();
    await redisClient.del(sessionId);
  }
}
  1. Real-time Pub-Sub: nestjs-redis supports the pub-sub messaging pattern, allowing applications to publish and subscribe to messages in real-time. This feature is beneficial for building event-driven architectures, real-time updates, and inter-service communication. By using Redis’s pub-sub functionality, developers can easily integrate real-time messaging capabilities into their Nest.js applications. Here’s an example of how to use pub-sub messaging with nestjs-redis:
import { Injectable } from '@nestjs/common';
import { RedisService } from 'nestjs-redis';

@Injectable()
export class MessageService {
  constructor(private readonly redisService: RedisService) {}

  async publishMessage(channel: string, message: string): Promise<void> {
    const redisClient = this.redisService.getClient();
    await redisClient.publish(channel, message);
  }

  async subscribeToChannel(channel: string, callback: (message: string) => void): Promise<void> {
    const redisClient = this.redisService.getClient();
    await redisClient.subscribe(channel, callback);
  }
}
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