NestJs Is not injecting value in jest unit test - unit-testing

Question

I cant figure out why nestjs is not injecting value into my contstructor
Controller
export class HealthCheckController {
constructor(#Inject('HealthCheckService') private healthCheckService: HealthCheckService, private appLogger: AppLogger) {
}
Then my test
beforeEach(async () => {
module = await Test.createTestingModule({
controllers: [HealthCheckController],
providers: [
AppLoggerNope.getProvider(),
{ provide: 'HealthCheckService', useClass: HealthCheckService },
],
})
.compile();
controller = await module.resolve<HealthCheckController>(HealthCheckController);
const logger = await module.resolve<AppLogger>(AppLogger);
service = await module.resolve<HealthCheckService>('HealthCheckService');
});
NopeLogger
export class AppLoggerNope {
static getProvider() {
return {
provide: AppLogger,
useValue: {}
}
}
}
So if I debug my test I can see that instance of service is supplied but logger is null.
Now what is interesting if I comment appLogger in provider controller will be created but it will fail await module.resolve<AppLogger>(AppLogger);

Answer 1

You don't need to explicitly define an injection token for the HealthCheckService with #Inject, Nest will resolve it for you. You also don't need to use module.resolve unless you're using request-scoped providers. I've also pulled out the provider from your AppLoggerNope static method for simplicity. If this is working, then you can start to get fancy and move those values elsewhere.
Controller:
export class HealthCheckController {
constructor(private healthCheckService: HealthCheckService, private appLogger: AppLogger) { }
Test file:
beforeEach(async () => {
module = await Test.createTestingModule({
controllers: [HealthCheckController],
providers: [
{ provide: AppLogger, useValue: {} },
HealthCheckService,
],
})
.compile();
controller = module.get<HealthCheckController>(HealthCheckController);
const logger = module.get<AppLogger>(AppLogger);
service = module.get<HealthCheckService>(HealthCheckService);
});
Note that the HealthCheckService is supplied directly as a provider in the testing module. Unless you need to mock something or stub out some kind of functionality, you can directly use it as a provider in your testing module. If you needed to be able to assert that some method within HealthCheckService was called in a test, you may want to do something like this:
const mockedHealthCheck = { someMethod: jest.fn() };
module = await Test.createTestingModule({
controllers: [HealthCheckController],
providers: [
{ provide: AppLogger, useValue: {} },
{ provide: HealthCheckService, useValue: mockedHealthCheck,
],
})
.compile();
Then in your test you can assert expect(mockedHealthCheck.someMethod).toBeCalled().