Allow editing persisted value stream

ee/app/models/analytics/cycle_analytics/group_value_stream.rb

@@ -13,6 +13,6 @@ class Analytics::CycleAnalytics::GroupValueStream < ApplicationRecord
   scope :preload_associated_models, -> { includes(:group, stages: [:group, :end_event_label, :start_event_label]) }
 
   def custom?
-    name != Analytics::CycleAnalytics::Stages::BaseService::DEFAULT_VALUE_STREAM_NAME
+    persisted? || name != Analytics::CycleAnalytics::Stages::BaseService::DEFAULT_VALUE_STREAM_NAME
   end
 end

ee/spec/controllers/groups/analytics/cycle_analytics/value_streams_controller_spec.rb

@@ -178,17 +178,6 @@ RSpec.describe Groups::Analytics::CycleAnalytics::ValueStreamsController do
       delete :destroy, params: { group_id: group, id: value_stream }
     end
 
-    context 'when it is a default value stream' do
-      let!(:value_stream) { create(:cycle_analytics_group_value_stream, group: group, name: 'default') }
-
-      it 'returns an unprocessable entity 422 response without deleting the value stream' do
-        expect { destroy_value_stream }.not_to change { Analytics::CycleAnalytics::GroupValueStream.count }
-
-        expect(response).to have_gitlab_http_status(:unprocessable_entity)
-        expect(json_response["message"]).to eq('The Default Value Stream cannot be deleted')
-      end
-    end
-
     context 'when it is a custom value stream' do
       let!(:value_stream) { create(:cycle_analytics_group_value_stream, group: group, name: 'some custom value stream') }
       let!(:stage) { create(:cycle_analytics_group_stage, value_stream: value_stream) }

ee/spec/factories/analytics/cycle_analytics/group_value_streams.rb

@@ -3,5 +3,7 @@
 FactoryBot.define do
   factory :cycle_analytics_group_value_stream, class: 'Analytics::CycleAnalytics::GroupValueStream' do
     sequence(:name) { |n| "Value Stream ##{n}" }
+
+    group
   end
 end

ee/spec/models/analytics/cycle_analytics/group_value_stream_spec.rb

@@ -45,4 +45,28 @@ RSpec.describe Analytics::CycleAnalytics::GroupValueStream, type: :model do
       end
     end
   end
+
+  describe '#custom?' do
+    context 'when value stream is not persisted' do
+      subject(:value_stream) { build(:cycle_analytics_group_value_stream, name: value_stream_name) }
+
+      context 'when the name of the value stream is default' do
+        let(:value_stream_name) { Analytics::CycleAnalytics::Stages::BaseService::DEFAULT_VALUE_STREAM_NAME }
+
+        it { is_expected.not_to be_custom }
+      end
+
+      context 'when the name of the value stream is not default' do
+        let(:value_stream_name) { 'value_stream_1' }
+
+        it { is_expected.to be_custom }
+      end
+    end
+
+    context 'when value stream is persisted' do
+      subject(:value_stream) { create(:cycle_analytics_group_value_stream, name: 'value_stream_1') }
+
+      it { is_expected.to be_custom }
+    end
+  end
 end