Create shared examples and helpers to test EventStore

Have a consistent way of testing publishing and consumption
of events.

doc/development/event_store.md

@@ -290,3 +290,43 @@ executed synchronously every time the given event is published.
 
 For complex conditions it's best to subscribe to all the events and then handle the logic
 in the `handle_event` method of the subscriber worker.
+
+## Testing
+
+A publisher doesn't must care what subscribed to the event being published. The publisher's
+responsibility is to ensure that the event is published correctly.
+
+To test that an event has been published correctly, we can use the RSpec matcher `:publish_event`:
+
+```ruby
+it 'publishes a ProjectDeleted event with project id and namespace id' do
+  expected_data = { project_id: project.id, namespace_id: project.namespace_id }
+
+  # The matcher verifies that when the block is called, the block publishes the expected event and data.
+  expect { destroy_project(project, user, {}) }
+    .to publish_event(Projects::ProjectDeletedEvent)
+    .with(expected_data)
+end
+```
+
+The subscriber must ensure that a published event can be consumed correctly. For this purpose
+we have added helpers and shared examples to standardize the way we test subscribers:
+
+```ruby
+RSpec.describe MergeRequests::UpdateHeadPipelineWorker do
+  let(:event) { Ci::PipelineCreatedEvent.new(data: ({ pipeline_id: pipeline.id })) }
+
+  # This shared example ensures that an event is published and correctly processed by
+  # the current subscriber (`described_class`).
+  it_behaves_like 'consumes the published event' do
+    let(:event) { event }
+  end
+  
+  it 'does something' do
+    # This helper directly executes `perform` ensuring that `handle_event` is called correctly.
+    consume_event(subscriber: described_class, event: event)
+
+    # run expectations
+  end
+end
+```

ee/spec/workers/geo/create_repository_updated_event_worker_spec.rb

@@ -11,17 +11,15 @@ RSpec.describe Geo::CreateRepositoryUpdatedEventWorker do
 
   let(:event) { Repositories::KeepAroundRefsCreatedEvent.new(data: { project_id: project.id }) }
 
-  subject { consume_event(event) }
-
-  def consume_event(event)
-    described_class.new.perform(event.class.name, event.data)
-  end
+  subject { consume_event(subscriber: described_class, event: event) }
 
   context 'on a Geo primary site' do
     before do
       stub_current_geo_node(primary_site)
     end
 
+    it_behaves_like 'subscribes to event'
+
     include_examples 'an idempotent worker' do
       let(:job_args) { [event.class.name, event.data] }
 

ee/spec/workers/security/findings/delete_by_job_id_worker_spec.rb

@@ -4,16 +4,18 @@ require 'spec_helper'
 
 RSpec.describe Security::Findings::DeleteByJobIdWorker do
   let(:job_ids) { [1, 2, 3] }
-  let(:event) { Ci::PipelineCreatedEvent.new(data: { job_ids: job_ids }) }
+  let(:event) { Ci::JobArtifactsDeletedEvent.new(data: { job_ids: job_ids }) }
 
-  subject(:consume_event) { described_class.new.perform(event.class.name, event.data) }
+  subject { consume_event(subscriber: described_class, event: event) }
 
   before do
     allow(::Security::Findings::CleanupService).to receive(:delete_by_build_ids)
   end
 
+  it_behaves_like 'subscribes to event'
+
   it 'initiates the cleanup by build ids' do
-    consume_event
+    subject
 
     expect(::Security::Findings::CleanupService).to have_received(:delete_by_build_ids).with(job_ids)
   end

spec/support/shared_examples/lib/gitlab/event_store_shared_examples.rb

+# frozen_string_literal: true
+
+RSpec.shared_examples 'subscribes to event' do
+  include AfterNextHelpers
+
+  it 'consumes the published event', :sidekiq_inline do
+    expect_next(described_class)
+      .to receive(:handle_event)
+      .with(instance_of(event.class))
+      .and_call_original
+
+    ::Gitlab::EventStore.publish(event)
+  end
+end
+
+def consume_event(subscriber:, event:)
+  subscriber.new.perform(event.class.name, event.data)
+end

spec/workers/merge_requests/update_head_pipeline_worker_spec.rb

@@ -11,11 +11,9 @@ RSpec.describe MergeRequests::UpdateHeadPipelineWorker do
   let(:pipeline) { create(:ci_pipeline, project: project, ref: ref) }
   let(:event) { Ci::PipelineCreatedEvent.new(data: { pipeline_id: pipeline.id }) }
 
-  subject { consume_event(event) }
+  subject { consume_event(subscriber: described_class, event: event) }
 
-  def consume_event(event)
-    described_class.new.perform(event.class.name, event.data)
-  end
+  it_behaves_like 'subscribes to event'
 
   context 'when merge requests already exist for this source branch', :sidekiq_inline do
     let(:merge_request_1) do

spec/workers/namespaces/update_root_statistics_worker_spec.rb

@@ -9,11 +9,9 @@ RSpec.describe Namespaces::UpdateRootStatisticsWorker do
     Projects::ProjectDeletedEvent.new(data: { project_id: 1, namespace_id: namespace_id })
   end
 
-  subject { consume_event(event) }
+  subject { consume_event(subscriber: described_class, event: event) }
 
-  def consume_event(event)
-    described_class.new.perform(event.class.name, event.data)
-  end
+  it_behaves_like 'subscribes to event'
 
   it 'enqueues ScheduleAggregationWorker' do
     expect(Namespaces::ScheduleAggregationWorker).to receive(:perform_async).with(namespace_id)