Respect DNT when tracking experiments

While we have not enabled experiments for users with DNT set to '1', we
were sending snowplow events and recorded the users within the control
group. This is not only against the idea of DNT, but also influences our
experimentation data.

changelogs/unreleased/nicolasdular-respect-dnt.yml

+---
+title: Respect DNT when tracking experiments
+merge_request: 44420
+author:
+type: fixed

lib/gitlab/experimentation.rb

@@ -114,18 +114,23 @@ module Gitlab
       end
 
       def track_experiment_event(experiment_key, action, value = nil)
+        return if dnt_enabled?
+
         track_experiment_event_for(experiment_key, action, value) do |tracking_data|
           ::Gitlab::Tracking.event(tracking_data.delete(:category), tracking_data.delete(:action), **tracking_data)
         end
       end
 
       def frontend_experimentation_tracking_data(experiment_key, action, value = nil)
+        return if dnt_enabled?
+
         track_experiment_event_for(experiment_key, action, value) do |tracking_data|
           gon.push(tracking_data: tracking_data)
         end
       end
 
       def record_experiment_user(experiment_key)
+        return if dnt_enabled?
         return unless Experimentation.enabled?(experiment_key) && current_user
 
         ::Experiment.add_user(experiment_key, tracking_group(experiment_key), current_user)

spec/lib/gitlab/experimentation_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe Gitlab::Experimentation do
+RSpec.describe Gitlab::Experimentation, :snowplow do
   before do
     stub_const('Gitlab::Experimentation::EXPERIMENTS', {
       test_experiment: {
@@ -141,13 +141,14 @@ RSpec.describe Gitlab::Experimentation do
           end
 
           it 'tracks the event with the right parameters' do
-            expect(Gitlab::Tracking).to receive(:event).with(
-              'Team',
-              'start',
+            controller.track_experiment_event(:test_experiment, 'start', 1)
+
+            expect_snowplow_event(
+              category: 'Team',
+              action: 'start',
               property: 'experimental_group',
-              value: 'team_id'
+              value: 1
             )
-            controller.track_experiment_event(:test_experiment, 'start', 'team_id')
           end
         end
 
@@ -157,13 +158,43 @@ RSpec.describe Gitlab::Experimentation do
           end
 
           it 'tracks the event with the right parameters' do
-            expect(Gitlab::Tracking).to receive(:event).with(
-              'Team',
-              'start',
+            controller.track_experiment_event(:test_experiment, 'start', 1)
+
+            expect_snowplow_event(
+              category: 'Team',
+              action: 'start',
               property: 'control_group',
-              value: 'team_id'
+              value: 1
             )
-            controller.track_experiment_event(:test_experiment, 'start', 'team_id')
+          end
+        end
+
+        context 'do not track is disabled' do
+          before do
+            request.headers['DNT'] = '0'
+          end
+
+          it 'does track the event' do
+            controller.track_experiment_event(:test_experiment, 'start', 1)
+
+            expect_snowplow_event(
+              category: 'Team',
+              action: 'start',
+              property: 'control_group',
+              value: 1
+            )
+          end
+        end
+
+        context 'do not track enabled' do
+          before do
+            request.headers['DNT'] = '1'
+          end
+
+          it 'does not track the event' do
+            controller.track_experiment_event(:test_experiment, 'start', 1)
+
+            expect_no_snowplow_event
           end
         end
       end
@@ -174,8 +205,9 @@ RSpec.describe Gitlab::Experimentation do
         end
 
         it 'does not track the event' do
-          expect(Gitlab::Tracking).not_to receive(:event)
           controller.track_experiment_event(:test_experiment, 'start')
+
+          expect_no_snowplow_event
         end
       end
     end
@@ -234,6 +266,36 @@ RSpec.describe Gitlab::Experimentation do
             )
           end
         end
+
+        context 'do not track disabled' do
+          before do
+            request.headers['DNT'] = '0'
+          end
+
+          it 'pushes the right parameters to gon' do
+            controller.frontend_experimentation_tracking_data(:test_experiment, 'start')
+
+            expect(Gon.tracking_data).to eq(
+              {
+                category: 'Team',
+                action: 'start',
+                property: 'control_group'
+              }
+            )
+          end
+        end
+
+        context 'do not track enabled' do
+          before do
+            request.headers['DNT'] = '1'
+          end
+
+          it 'does not push data to gon' do
+            controller.frontend_experimentation_tracking_data(:test_experiment, 'start')
+
+            expect(Gon.method_defined?(:tracking_data)).to be_falsey
+          end
+        end
       end
 
       context 'when the experiment is disabled' do
@@ -308,6 +370,39 @@ RSpec.describe Gitlab::Experimentation do
           controller.record_experiment_user(:test_experiment)
         end
       end
+
+      context 'do not track' do
+        before do
+          allow(controller).to receive(:current_user).and_return(user)
+          allow_next_instance_of(described_class) do |instance|
+            allow(instance).to receive(:experiment_enabled?).with(:test_experiment).and_return(false)
+          end
+        end
+
+        context 'is disabled' do
+          before do
+            request.headers['DNT'] = '0'
+          end
+
+          it 'calls add_user on the Experiment model' do
+            expect(::Experiment).to receive(:add_user).with(:test_experiment, :control, user)
+
+            controller.record_experiment_user(:test_experiment)
+          end
+        end
+
+        context 'is enabled' do
+          before do
+            request.headers['DNT'] = '1'
+          end
+
+          it 'does not call add_user on the Experiment model' do
+            expect(::Experiment).not_to receive(:add_user)
+
+            controller.record_experiment_user(:test_experiment)
+          end
+        end
+      end
     end
 
     describe '#experiment_tracking_category_and_group' do