Message Pact is non Http approach, see for more details: https://docs.pact.io/getting_started/how_pact_works#non-http-testing-message-pact
ActiveSupport::Notification - is part of [Rails ActiveSupport][1], see for more details: https://apidock.com/rails/ActiveSupport/Notifications
As I understand, ActiveSupport::Notification is using memory for a queue underneath, but not the external requests that are expected by Pact, so probably it can be done only via some other Message Queue, like Kafka, for example:
ActiveSupport::Notifications.subscribe("my_message") do |payload|
Kafka.produce(queue: 'test-queue', message: payload)
end
where Kafka.produce can be handled by Pact.
However, in this way, there is makes sense to remove ActiveSupport::Notifications and keep using only Kafka but this is the next step.