Track issues to epics promotions

- track promotiones from issue to epic from a service
- add check if a snowplow cagetory is supported

ee/app/services/epics/issue_promote_service.rb

@@ -17,11 +17,18 @@ module Epics
 
       super
 
+      track_event
       new_entity
     end
 
     private
 
+    def track_event
+      ::Gitlab::SnowplowTracker.track_event(
+        'epics', 'promote', property: 'issue_id', value: original_entity.id
+      )
+    end
+
     def create_new_entity
       @new_entity = Epics::CreateService.new(@group, current_user, params).execute
     end

ee/lib/gitlab/snowplow_tracker.rb

@@ -8,9 +8,7 @@ module Gitlab
 
     class << self
       def track_event(category, action, label: nil, property: nil, value: nil, context: nil)
-        return unless enabled?
-
-        tracker.track_struct_event(category, action, label, property, value, context, Time.now.to_i)
+        tracker&.track_struct_event(category, action, label, property, value, context, Time.now.to_i)
       end
 
       private

ee/spec/lib/gitlab/snowplow_tracker_spec.rb

@@ -8,7 +8,7 @@ describe Gitlab::SnowplowTracker do
     Timecop.freeze(timestamp) { example.run }
   end
 
-  subject { described_class.track_event('category', 'action', property: 'what', value: 'doit') }
+  subject { described_class.track_event('epics', 'action', property: 'what', value: 'doit') }
 
   context '.track_event' do
     context 'when Snowplow tracker is disabled' do
@@ -20,10 +20,13 @@ describe Gitlab::SnowplowTracker do
     end
 
     context 'when Snowplow tracker is enabled' do
-      it 'tracks the event' do
+      before do
         stub_application_setting(snowplow_enabled: true)
         stub_application_setting(snowplow_site_id: 'awesome gitlab')
         stub_application_setting(snowplow_collector_uri: 'url.com')
+      end
+
+      it 'tracks the event' do
         tracker = double
 
         expect(::SnowplowTracker::Tracker).to receive(:new)
@@ -33,7 +36,7 @@ describe Gitlab::SnowplowTracker do
             'cf', 'awesome gitlab'
           ).and_return(tracker)
         expect(tracker).to receive(:track_struct_event)
-          .with('category', 'action', nil, 'what', 'doit', nil, timestamp.to_i)
+          .with('epics', 'action', nil, 'what', 'doit', nil, timestamp.to_i)
 
         subject
       end

ee/spec/services/epics/issue_promote_service_spec.rb

@@ -56,6 +56,8 @@ describe Epics::IssuePromoteService do
 
         context 'when issue is promoted' do
           before do
+            allow(Gitlab::SnowplowTracker).to receive(:track_event).with('epics', 'promote', an_instance_of(Hash))
+
             subject.execute(issue)
           end