运行NestJS测试用例时出现I18nService依赖注入错误

运行NestJS测试用例时出现依赖解析错误，Nest无法找到I18nService所需的I18nOptions等依赖项，报错提示需确保这些依赖在I18nService上下文可用。

测试代码 #

import { Test } from '@nestjs/testing';

import { appConfig } from '../app.config';
import { CommonBotModule } from '../common/common-bot.module';
import { CredentialsManagerModule } from '../credentials/credentials-manager.module';
import { BotModule } from './bot.module';
import { I18nService } from 'nestjs-i18n';

jest.mock('aws-sdk'); // 阻止连接DynamoDB
jest.mock('@aws/dynamodb-data-mapper'); // 阻止连接DynamoDB
jest.mock('kafkajs');
jest.mock('../cache/cacheConfig.service'); // 阻止连接Redis

describe('bot.module.ts', () => {
    beforeAll(() => {
        config.init(appConfig);
    });

    it('The bot module should be able to be compiled', async () => {
        const botModule = await Test.createTestingModule({
            imports: [CommonBotModule, CredentialsManagerModule, BotModule, I18nService]
        }).compile();

        expect(botModule).toBeDefined();
    });
});

错误日志 #

Nest can't resolve dependencies of the I18nService (?, I18nTranslations, I18nLanguages, Logger, I18nLoader, I18nLanguagesSubject, I18nTranslationsSubject). Please make sure that the argument I18nOptions at index [0] is available in the I18nService context.

    Potential solutions:
    - If I18nOptions is a provider, is it part of the current I18nService?
    - If I18nOptions is exported from a separate @Module, is that module imported within I18nService?
      @Module({
        imports: [ /* the Module containing I18nOptions */ ]
      })

问题原因与修复方案 #

核心问题 #

测试代码中错误地将I18nService放入了imports数组——imports只能存放用@Module装饰的模块类，而I18nService是一个服务提供者，不能直接导入到这里。Nest无法找到I18nService依赖的I18nOptions，因为没有正确引入提供这些依赖的模块。

修复方式（二选一） #

方式1：模拟I18nService（推荐测试环境使用）

通过jest.mock模拟I18nService，避免初始化真实的服务和依赖：

import { Test } from '@nestjs/testing';

import { appConfig } from '../app.config';
import { CommonBotModule } from '../common/common-bot.module';
import { CredentialsManagerModule } from '../credentials/credentials-manager.module';
import { BotModule } from './bot.module';
import { I18nService } from 'nestjs-i18n';

jest.mock('aws-sdk');
jest.mock('@aws/dynamodb-data-mapper');
jest.mock('kafkajs');
jest.mock('../cache/cacheConfig.service');

// 模拟I18nService及其方法
jest.mock('nestjs-i18n', () => ({
  ...jest.requireActual('nestjs-i18n'),
  I18nService: jest.fn().mockImplementation(() => ({
    translate: jest.fn().mockReturnValue('模拟翻译内容')
  }))
}));

describe('bot.module.ts', () => {
    beforeAll(() => {
        config.init(appConfig);
    });

    it('The bot module should be able to be compiled', async () => {
        const botModule = await Test.createTestingModule({
            imports: [CommonBotModule, CredentialsManagerModule, BotModule]
            // 移除imports中的I18nService
        }).compile();

        expect(botModule).toBeDefined();
    });
});

方式2：导入并配置I18nModule

如果测试需要真实的I18n功能，在测试模块中导入并配置I18nModule：

import { Test } from '@nestjs/testing';
import { I18nModule } from 'nestjs-i18n';
import * as path from 'path';

import { appConfig } from '../app.config';
import { CommonBotModule } from '../common/common-bot.module';
import { CredentialsManagerModule } from '../credentials/credentials-manager.module';
import { BotModule } from './bot.module';

jest.mock('aws-sdk');
jest.mock('@aws/dynamodb-data-mapper');
jest.mock('kafkajs');
jest.mock('../cache/cacheConfig.service');

describe('bot.module.ts', () => {
    beforeAll(() => {
        config.init(appConfig);
    });

    it('The bot module should be able to be compiled', async () => {
        const botModule = await Test.createTestingModule({
            imports: [
                CommonBotModule, 
                CredentialsManagerModule, 
                BotModule,
                // 配置测试用的I18nModule
                I18nModule.forRoot({
                    fallbackLanguage: 'en',
                    loaderOptions: {
                        path: path.join(__dirname, '../i18n'),
                        watch: false
                    }
                })
            ]
        }).compile();

        expect(botModule).toBeDefined();
    });
});

内容的提问来源于stack exchange，提问作者Nishad Mahajan