How to write automated tests for asynchronous micro services?

Our system deals with a lot of third party integrations and usage of queues and caching

Ex: X api calls Y api , Y api updates Mongo DB and calls 3rd party api , Every 2 hours one cron runs and checks if call back is received , then events are posted to kafka queues and cache is updated with latest data from call back etc and goes on

If I want to write automation then non-deterministic behaviour of the system becomes a hurdle .

So how can I write a scalable automation ? What should be my approach ? Is there any article available which has already posted on this ?