NestJS运行E2E测试时出现Reflect.getMetadata TypeError的解决咨询

报错信息 #

[Nest] 163363  - 10/03/2022, 11:59:37 AM     LOG [NestFactory] Starting Nest application...
[Nest] 163363  - 10/03/2022, 11:59:37 AM   ERROR [ExceptionHandler] 
TypeError
    at Reflect.getMetadata (/home/mszan/foo/source/node_modules/reflect-metadata/Reflect.js:354:23)
    at DependenciesScanner.isInjectable (/home/mszan/foo/source/node_modules/@nestjs/core/scanner.js:302:26)
    at DependenciesScanner.insertModule (/home/mszan/foo/source/node_modules/@nestjs/core/scanner.js:73:18)
    at DependenciesScanner.scanForModules (/home/mszan/foo/source/node_modules/@nestjs/core/scanner.js:34:43)
    at DependenciesScanner.scan (/home/mszan/foo/source/node_modules/@nestjs/core/scanner.js:27:20)
    at async /home/mszan/foo/source/node_modules/@nestjs/core/nest-factory.js:95:17
    at async Function.asyncRun (/home/mszan/foo/source/node_modules/@nestjs/core/errors/exceptions-zone.js:22:13)
    at async NestFactoryStatic.initialize (/home/mszan/foo/source/node_modules/@nestjs/core/nest-factory.js:94:13)
    at async NestFactoryStatic.create (/home/mszan/foo/source/node_modules/@nestjs/core/nest-factory.js:37:9)
  ●  process.exit called with "1"

      at DEFAULT_TEARDOWN (../../node_modules/@nestjs/core/errors/exceptions-zone.js:6:40)
      at Function.asyncRun (../../node_modules/@nestjs/core/errors/exceptions-zone.js:29:13)
      at async NestFactoryStatic.initialize (../../node_modules/@nestjs/core/nest-factory.js:94:13)
      at async NestFactoryStatic.create (../../node_modules/@nestjs/core/nest-factory.js:37:9)

测试代码（app.e2e-spec.ts） #

describe('app - e2e', () => {
    let app: INestApplication;

    beforeAll(async () => {
        const moduleRef: TestingModule = await Test.createTestingModule({
            ...appModuleMetadata,
            imports: appModuleMetadata.imports.map((x) => {
                if (x == CommonModule) {
                    return CommonModuleMock;
                }
                return x;
            }),
        }).compile();
        app = moduleRef.createNestApplication();
        await app.init();
    });
});

问题详情 #

CommonModule包含一个依赖fs和path包的Provider，移除这些依赖后测试可正常运行。但尝试用不含上述依赖的CommonModuleMock替换原CommonModule时，测试仍抛出上述错误。当前环境版本：Nest 9.0.11、Jest 29.0.3、Supertest 6.2.4、Node 16.17.0。

解决选项 #

• 检查CommonModuleMock的模块定义规范：确保Mock模块用@Module()装饰器正确包裹，内部的Provider、导出项等配置符合NestJS模块要求。如果Mock模块结构不合法，依赖扫描器会无法识别，抛出Reflect相关错误。
• 改用overrideModule替换模块：放弃手动遍历imports数组的方式，使用NestJS测试工具提供的overrideModuleAPI，更可靠地替换目标模块：

  const moduleRef: TestingModule = await Test.createTestingModule(appModuleMetadata)
    .overrideModule(CommonModule)
    .useModule(CommonModuleMock)
    .compile();
  

• 排查Mock模块的间接依赖：检查CommonModuleMock的imports或Provider是否意外引入了原CommonModule的内容，导致原模块的fs/path依赖仍被加载。
• 清理Jest缓存：Jest可能缓存了旧的模块编译结果，执行jest --clearCache后重新运行测试，排除缓存导致的问题。
• 校验reflect-metadata版本兼容性：NestJS 9对reflect-metadata有版本要求，确保项目中该包的版本与@nestjs/core兼容，可尝试重新安装依赖：rm -rf node_modules package-lock.json && npm install。
• 仅Mock问题Provider而非整个模块：如果替换整个模块成本高，可只MockCommonModule中依赖fs/path的那个Provider，保留模块其他部分：

  const moduleRef: TestingModule = await Test.createTestingModule(appModuleMetadata)
    .overrideProvider(ProblematicProvider)
    .useValue(mockProviderInstance)
    .compile();
  

内容的提问来源于stack exchange，提问作者mszan