Track events for paid signup flow

Adds tracking when starting and completing the new sign up flow
to snowplow.

ee/app/controllers/subscriptions_controller.rb

@@ -24,10 +24,12 @@ class SubscriptionsController < ApplicationController
 
   def new
     if experiment_enabled?(:paid_signup_flow)
-      return if current_user
-
-      store_location_for :user, request.fullpath
-      redirect_to new_user_registration_path
+      if current_user
+        track_paid_signup_flow_event('start')
+      else
+        store_location_for :user, request.fullpath
+        redirect_to new_user_registration_path
+      end
     else
       redirect_to customer_portal_new_subscription_url
     end
@@ -57,12 +59,30 @@ class SubscriptionsController < ApplicationController
       subscription_params: subscription_params
     ).execute
 
-    response[:data] = { location: edit_subscriptions_group_path(group.path) } if response[:success]
+    if response[:success]
+      response[:data] = { location: edit_subscriptions_group_path(group.path) }
+
+      track_paid_signup_flow_event(
+        'end',
+        label: subscription_params[:plan_id],
+        value: subscription_params[:quantity]
+      )
+    end
+
     render json: response[:data]
   end
 
   private
 
+  def track_paid_signup_flow_event(action, label: nil, value: nil)
+    ::Gitlab::Tracking.event(
+      'Growth::Acquisition::Experiment::PaidSignUpFlow',
+      action,
+      label: label,
+      value: value
+    )
+  end
+
   def customer_params
     params.require(:customer).permit(:country, :address_1, :address_2, :city, :state, :zip_code, :company)
   end

ee/spec/controllers/subscriptions_controller_spec.rb

@@ -32,6 +32,12 @@ describe SubscriptionsController do
 
         it { is_expected.to render_template 'layouts/checkout' }
         it { is_expected.to render_template :new }
+
+        it 'tracks the event with the right parameters' do
+          expect(Gitlab::Tracking).to receive(:event).with('Growth::Acquisition::Experiment::PaidSignUpFlow', 'start', label: nil, value: nil)
+
+          subject
+        end
       end
     end
 
@@ -96,14 +102,18 @@ describe SubscriptionsController do
   describe 'POST #create' do
     subject do
       post :create,
-        params: {
-          setup_for_company: setup_for_company,
-          customer: { company: 'My company', country: 'NL' },
-          subscription: { plan_id: 'x' }
-        },
+        params: params,
         as: :json
     end
 
+    let(:params) do
+      {
+        setup_for_company: setup_for_company,
+        customer: { company: 'My company', country: 'NL' },
+        subscription: { plan_id: 'x', quantity: 2 }
+      }
+    end
+
     let(:setup_for_company) { true }
 
     context 'with unauthorized user' do
@@ -124,14 +134,44 @@ describe SubscriptionsController do
         it 'updates the setup_for_company attribute of the current user' do
           expect { subject }.to change { user.reload.setup_for_company }.from(nil).to(true)
         end
+
+        it 'tracks the event with the right parameters' do
+          expect(Gitlab::Tracking).to receive(:event).with(
+            'Growth::Acquisition::Experiment::PaidSignUpFlow',
+            'end',
+            label: 'x',
+            value: 2
+          )
+
+          subject
+        end
       end
 
       context 'when not setting up for a company' do
+        let(:params) do
+          {
+            setup_for_company: setup_for_company,
+            customer: { country: 'NL' },
+            subscription: { plan_id: 'x', quantity: 1 }
+          }
+        end
+
         let(:setup_for_company) { false }
 
         it 'does not update the setup_for_company attribute of the current user' do
           expect { subject }.not_to change { user.reload.setup_for_company }
         end
+
+        it 'tracks the event with the right parameters' do
+          expect(Gitlab::Tracking).to receive(:event).with(
+            'Growth::Acquisition::Experiment::PaidSignUpFlow',
+            'end',
+            label: 'x',
+            value: 1
+          )
+
+          subject
+        end
       end
 
       it 'creates a group' do