V3 - Messages / Events upgrade

[monsieurblibble]

Hey,
While upgrading to V3 of pact-python, I was unable to find the equivalent to the V2 "MessagePact" system.
I had a look in the migration guide, implementation guides, and examples in the pact-python repo.

Looking through other language specific implementations, I noticed other functionality e.g. Go's "Event driven-system";
This would be ideal for me - I was using the previous "MessagePact" system in a similar way.

Looking at the feature support it says this functionality is supported for Python (Async and Sync Messaging) - but this page hasn't been updated since 2024 (before V3 came out).

Is there a way to implement this functionality since V3 has come out?
Hopefully I'm just missing something obvious!

Thanks,
Flibble

[JP-Ellis]

Thanks for the question! It is on my todo list to add clear docs on how event driven systems can/should be tested.

In the meantime though, I hope that the API docs will suffice. In particular:

1. You can define an async or synchronous message interaction as part of the upon_receiving call:

   upon_receiving(
       description: str, interaction: Literal["Async"]
   ) -> AsyncMessageInteraction

   upon_receiving(
       description: str, interaction: Literal["Sync"]
   ) -> SyncMessageInteraction

2. These return an AsyncMessageInteraction or a SyncMessageInteraction which follow generally quite similar patterns to your HTTP method when it comes to defining the interaction itself

When it comes to the verification, you can pass in a handler to Pact.verify.

There is a slightly outdated example for testing a message consumer and provider. I am yet to migrate these examples to the new directory structure of the current examples.

Please let me know if that helps!

[monsieurblibble]

thanks for the quick reply!!

I'll have a look into it,
but this seems to answer my question! (I'll try it out and update the thread)

having a look through it, it seems MessageInteraction could be used to support generic interactions also;
do you think you'd be able to support event-based interactions using this, for example?
(e.g. one service creates a resource on a shared space (with which a listener in another service interacts), similarly for DB changes, or custom request formats e.g. signal inputs, etc.)
perhaps by using custom handlers when defining the interaction?

I like the changes btw, I think they're positive overall!
Hopefully my follow up questions aren't silly - though they might be a tad off topic for this Q/A!

[JP-Ellis]

No at all silly questions! Glad you ask them, it'll help me when I write the docs :)

MessageInteraction could be used to support generic interactions also

That is absolutely correct. The Sync and Async variants abstract away the protocol and focus on verifying payload and, if available/needed, metadata. The main difference between the two is that Async has no response, where Sync does have one.

An example of an Async interaction would be your typical pub/sub model, event queues, notification topics, etc. The Sync interaction then builds on that by validating a response as well (though that is not as common).

Since we abstract away the protocol, we need to use handlers to pass in/out the payloads themselves. So Pact does not interact with AWS SQS/MQTT/etc. at all, you still have to handle/mock that, but we can validate the payloads.

(And sorry I didn't see your reply last week)

[monsieurblibble]

that's perfect, thanks!!
exactly what I was looking for!

enjoy the holidays (if you celebrate) - I'll mark this as resolved