Projection testing

Axon provides fixtures when it comes to Saga and Aggregate testing. When it comes to projection testing developers are left on their own. It might be useful to provide a functionality in axon-test module for testing projections.

Here is a proposal:

ProjectionFixture fixture = ProjectionFixture.registerHandlingComponent(new MyProjection()) // here we can have scanning of @EventHandlers and @QueryHandlers
                                             .registerResource(new MyRepository()); // or mock

fixture.given(events)
       .whenQuery(query) // whenScatterGatherQuery, whenSubscriptionQuery
       .expectResult(queryResult);

...

fixture.given(events)
       .andSubscriptionQuery(query) 
       .when(event)
       .expectEmittedUpdate(anUpdate);

[Blackdread]

big +1 I was looking to test queries but not possible

[hsdmiranda]

Yes, it is a bit frustrating to try to use the @QueryHandler/QueryGatway without testing support from the framework