如何通过传递带有自定义值的ConfigService来测试nestjs服务？

Question

我创建了一个服务，它的模块如下所示：

launchdarkly.module.ts

@Module({
  providers: [LaunchdarklyService],
  exports: [LaunchdarklyService],
  imports: [ConfigService],
})
export class LaunchdarklyModule {}

(这个服务/模块是让应用程序使用LaunchDarkly特性标记)

如果您愿意的话，我很高兴向您展示服务实现，但是为了缩短这个问题，我跳过了它。重要的一点是，该服务导入ConfigService (它用于获取LaunchDarkly SDK键)。

但是如何测试Launchdarkly服务呢？它从ConfigService中读取一个键，因此我想编写ConfigService具有不同值的测试，但经过几个小时的尝试，我无法在测试中找到如何配置ConfigService。

下面是一个测试：

launchdarkly.service.spec.ts

describe('LaunchdarklyService', () => {
  let service: LaunchdarklyService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [LaunchdarklyService],
      imports: [ConfigModule],
    }).compile();

    service = module.get<LaunchdarklyService>(LaunchdarklyService);
  });

  it("should not create a client if there's no key", async () => {
    // somehow I need ConfigService to have key FOO=undefined for this test
    expect(service.client).toBeUndefined();
  });

  it("should create a client if an SDK key is specified", async () => {
    // For this test ConfigService needs to specify FOO=123
    expect(service.client).toBeDefined();
  });
})

我愿意接受任何无伤大雅的建议，我只想把我的应用程序标记出来！

Answer 1

假设LaunchdarklyService需要ConfigService并将其注入构造函数，则可以通过使用Custom Provider返回所需的自定义凭据来提供ConfigService的模拟变体。例如，您的测试的模拟可能如下所示

describe('LaunchdarklyService', () => {
  let service: LaunchdarklyService;
  let config: ConfigService;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [LaunchdarklyService, {
        provide: ConfigService,
        useValue: {
          get: jest.fn((key: string) => {
            // this is being super extra, in the case that you need multiple keys with the `get` method
            if (key === 'FOO') {
              return 123;
            }
            return null;
          })
        }
      ],
    }).compile();

    service = module.get<LaunchdarklyService>(LaunchdarklyService);
    config = module.get<ConfigService>(ConfigService);
  });

  it("should not create a client if there's no key", async () => {
    // somehow I need ConfigService to have key FOO=undefined for this test
    // we can use jest spies to change the return value of a method
    jest.spyOn(config, 'get').mockReturnedValueOnce(undefined);
    expect(service.client).toBeUndefined();
  });

  it("should create a client if an SDK key is specified", async () => {
    // For this test ConfigService needs to specify FOO=123
    // the pre-configured mock takes care of this case
    expect(service.client).toBeDefined();
  });
})

Answer 2

您不需要提供ConfigService，而是需要导入带有模拟数据的ConfigModule。作为一个例子

imports: [CommonModule,ConfigModule.forRoot({
                ignoreEnvVars: true,
                ignoreEnvFile: true,
                load: [() => ({ IntersectionOptions: { number_of_decimal_places: '3' }})],
            })],