Motivation: I want to ensure on my E2E tests that I'm not retrying events that are not supposed to be retried, such as malformed events and events with business errors. The best place to ensure it is by spying the Controller's method annotated by EventPattern.
Results:
- ❌
spy controller instance- event is handled but spy does not track method call - ❌
spy controller prototype before init- event is not handled and as consequence test fails - ❌
spy controller prototype after init- event is handled but spy does not track method call
From a similar issue nestjs#8790 it states that:
Long story short: you can spy on/mock service methods. You can't spy on/mock controller methods (annotated methods) after your app is initialized (execution context is created).
From this statement, I concluded that spying on controller's annotated method has some dependency over execution context, so spying on its prototype should work, but in practice it's not.
It runs e2e tests by spinning up Kafka using TestContainers, starting NestJS application, publishing events, waiting for handling and then making assertions.
Install dependencies and run e2e tests:
npm install
npm run test:e2e
npm run test:e2e -- -t 'should spy controller instance'
npm run test:e2e -- -t 'should spy controller prototype before init'
npm run test:e2e -- -t 'should spy controller prototype after init'
Starting Kafka and application:
docker compose up -d
npm start:dev
Producing messages:
npm run produce
You can also visit KafkaUI at: http://localhost:8080