Testing domain logic

Specify the expected events to be published as a result of the given command. Simple!

CoffeeScript

describe 'MyNamespace.myBoundedContext.MyAggregate', ->
  beforeEach ->
    @app = new MyApp()
    @app.start()
    @aggregateId = new Guid()
    @data = {
      someValue: 'TestValue'
    }
    @anotherValue = 'TestValue2'
  it 'generates the MyAggregate created event', ->
    @app.given(
        new MyNamespace.myBoundedContext.CreateMyAggregate _.extend {}, @data, {
          targetId: @aggregateId
          timestamp: new Date()
        }
      )
      .expect([
        new MyNamespace.MyAggregateCreated _.extend {}, @data, {
          sourceId: @aggregateId
        }
      ])
      
    it 'generates the MyAggregate created event', ->
    @app.given(
        new MyNamespace.MyAggregateCreated _.extend {}, @data, {
          sourceId: @aggregateId
          timestamp: new Date()
        }
      )
      .when([
        new MyNamespace.myBoundedContext.DoSomething({
          targetId: @aggregateId
          timestamp: new Date()
          someValue: @anotherValue
        }) 
      ])
      .expect([
        new MyNamespace.MyAggregateChanged _.extend {}, @data, {
          sourceId: @aggregateId
        }
      ])

📘

What about unit testing in the domain?

One advantage of an event-sourced system based on the CQRS pattern is we can effectively omit fine-grained and arguably brittle unit tests since we really only need to check the events generated as a result of a command being sent in on the Command Bus. The messaging and event-sourcing libraries provide test coverage for reliable delivery, so you can focus on writing tests that ensure the aggregates are delivering the business requirements and are protecting themselves from invariants.