NestJS Memory Transport

This package aims to replace existing NestJS transport layers with a memory-based implementation. This is useful for testing purposes, as it allows you to run your application in memory without the need for a network connection. Specifically, it allows you to write in-process acceptance tests for a monorepo that consists of multiple microservices, without going out of process.

Installation

$ npm install nest-memory-transport

Getting Started

In order to replace existing transports such as Kafka or TCP, you'll need to restructure your NestJS application to allow injection of the transport layer from the outside.

Server

Assuming that your init code looks something like this:

async function bootstrap() {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(
    MyMicroserviceModule,
    {
      transport: Transport.KAFKA,
      options: {
        client: {
          clientId: 'some-client-id',
          brokers: ['localhost:9092'],
        },
        consumer: {
          groupId: 'some-consumer',
        },
      },
    },
  );
  await app.listen();
}
bootstrap();

with this:

// app.ts
export async function bootstrap(transportOptions: MicroserviceOptions) {
  const app = await NestFactory.createMicroservice<MicroserviceOptions>(
    MyMicroserviceModule,
    transportOptions,
  );
  await app.listen();
}

// main.ts
bootstrap({
  transport: Transport.KAFKA,
  options: {
    client: {
      clientId: 'some-client-id',
      brokers: ['localhost:9092'],
    },
    consumer: {
      groupId: 'some-consumer',
    },
  },
});

Then in your test, initialize the same microservice with the memory transport:

const emitter = new EventEmitter();
const myMicroService = await bootstrap({
  strategy: new MemoryTransportServer(emitter)
});

Client

Convert your AppModule to a DynamicModule that takes the transport layer as a parameter:

export class AppModule {
  static register(transport: DynamicModule): DynamicModule {
    return {
      imports: [transport, ...any other imports],
      controllers: [...your controllers],
      providers: [...your providers],
      module: AppModule,
    };
  }
}

In your main.ts, initialize the app with the production transport:

export async function bootstrap() {
  const app = await NestFactory.create(
    AppModule.register(
      ClientsModule.register([
        {
          name: 'KAFKA_CLIENT',
          transport: Transport.KAFKA,
          options: {
            client: {
              clientId: 'some-client-id',
              brokers: ['localhost:9092'],
            },
            consumer: {
              groupId: 'some-consumer',
            },
          },
        },
      ]),
    ),
  );
  await app.listen(3000);
  return app;
}

Then in your test, initialize the same app with the memory transport:

const appTestingModule = await Test.createTestingModule({ 
  imports: [AppModule.register(MemoryClientsModule.register({
    name: 'KAFKA_CLIENT',
    emitter, // the same emitter declared earlier, shared between all microservices and their clients
  }))],
}).compile();
await appTestingModule.createNestApplication().init();

See the e2e test for a full working example.

Issues

Ideally, add a failing test to any issue you submit.

Contributing

If you wish to contribute, please open a PR with a failing test, then implement the feature and make the test pass.