Merge branch '292032-force-experiments-to-persist-in-session' into 'master'

Force multiple experiments in browser session

See merge request gitlab-org/gitlab!49373

doc/development/experiment_guide/index.md

@@ -337,6 +337,27 @@ to the URL:
 https://gitlab.com/<EXPERIMENT_ENTRY_URL>?force_experiment=<EXPERIMENT_KEY>
 ```
 
+### A cookie-based approach to force an experiment
+
+It's possible to force the current user to be in the experiment group for <EXPERIMENT_KEY> 
+during the browser session by using your browser's developer tools:
+
+```javascript
+document.cookie = "force_experiment=<EXPERIMENT_KEY>; path=/";
+```
+
+Use a comma to list more than one experiment to be forced:
+
+```javascript
+document.cookie = "force_experiment=<EXPERIMENT_KEY>,<ANOTHER_EXPERIMENT_KEY>; path=/";
+```
+
+Clear the experiments by unsetting the `force_experiment` cookie:
+
+```javascript
+document.cookie = "force_experiment=; path=/";
+```
+
 ### Testing and test helpers
 
 #### RSpec

lib/gitlab/experimentation/controller_concern.rb

@@ -130,7 +130,10 @@ module Gitlab
       end
 
       def forced_enabled?(experiment_key)
-        params.has_key?(:force_experiment) && params[:force_experiment] == experiment_key.to_s
+        return true if params.has_key?(:force_experiment) && params[:force_experiment] == experiment_key.to_s
+        return false if cookies[:force_experiment].blank?
+
+        cookies[:force_experiment].to_s.split(',').any? { |experiment| experiment.strip == experiment_key.to_s }
       end
 
       def tracking_label(subject)

spec/lib/gitlab/experimentation/controller_concern_spec.rb

@@ -156,6 +156,16 @@ RSpec.describe Gitlab::Experimentation::ControllerConcern, type: :controller do
         is_expected.to eq(true)
       end
     end
+
+    context 'Cookie parameter to force enable experiment' do
+      it 'returns true unconditionally' do
+        cookies[:force_experiment] = 'test_experiment,another_experiment'
+        get :index
+
+        expect(check_experiment(:test_experiment)).to eq(true)
+        expect(check_experiment(:another_experiment)).to eq(true)
+      end
+    end
   end
 
   describe '#track_experiment_event', :snowplow do