Message Consumer and Provider Example

Contracts can also be developed by the consumers of asynchronous messages. We will want to expect messages from the consumers and verify that the providers will send the right messages. With asynchronous messaging, there will be no request portion to the test but only an incoming message to process. Likewise, for the provider, we will not receive any request for a message, so the testing pattern changes slightly.

Messaging contract testing with Pact

We will create tests for the messages that the Store Management module publishes, and test message consumption in both the Shopping Baskets and Depot modules.

The consumer tests are located in the /baskets/internal/handlers/integration_event_contract_test.go and /depot/internal/handlers/integration_event_contract_test.go files. These two modules receive messages from the Store Management module, which we will discuss later.

For each message that a consumer expects to receive, we must create an expected message entry in our contract with the following code: