Is there a formalization to add and validate constraints on the valid intervals in which particular events can be emitted in the system? I mean there might be multiple services/objects around waiting for messages and due the combinatorical explosion we can't enumerate all the possible sequences of events. I just can't believe there is no standard/proven way/know how to generate event sequences in any programming language. To me it seems it should be part of the testing libs maybe with additional abstractions for expressing the distinct "services"/"objects", but I don't see the need for a separate programming language for that, but still, I am not aware if that in the mainstream. I am wondering why is that.

What would be the use case/domain this would be applied to? Something like a state machine?

What kind of events? I assume you're not taking about code triggered events, since those can be triggered by code. Java has something called "Robot" which lets you control the mouse and keyboard programmatically (for "testing purposes")

Is there a formalization to add and validate constraints on the valid intervals in which particular events can be emitted in the system?

This sounds like the raison d'être of state machines.

@Cole just general verification. Yes exactly, I imagine a service/object like a state machine and my problem is that if there is a lot of them on top level then it is quite impossible to introduce a top level state machine (like hieararchical) without the combinatorical explosion 💥 . What I would like to do instead is add constraints on the valid ordering of events and 1. I would make sure the code really implements it. (Eg. if there is a constraint like: the eventstream can start off with E1 or there won't be any E1 in stream; I make sure the service emitting E1 is the first to emit events in my implementation and there is no other valid context in which the service is prompted to emit E1) 2. I would enumerate all the eventstreams(event ordering) with the constrains to make sure there is no ordering I missed / I forgot about. It reminds me a lot to automata theory/regexes, but to me they are closer to state machines. To me state machines are "clean" and easy and what I am looking for is how to make "cleaner" the "dirty (combinatorical) space above top level clean state machines" via temporal constrains. By temporal I mean constraints on ordering (check out Temporal Logic, especially Computational Tree Logic). I deeply believe adding/expressing constraints on ordering is REALLY easy compared to other techniques for verification. Furthermore, constraints on ordering of events has a lot to do the meaning of the software (for me), and it seems nice to me to make it explicit.

i had this same issue trying to apply property testing to the reducer of an event sourcing system. it would have been cool to generate valid event sequences for the purpose of testing the change in state that should be produced by a new command

That is exactly my wannabe usecase