v3(services): update should check new plan relates to same service offering

[#171670120]

Author: blgm

app/controllers/v3/service_instances_controller.rb

@@ -216,6 +216,7 @@ def update_managed(service_instance)
     if message.service_plan_guid
       service_plan = ServicePlan.first(guid: message.service_plan_guid)
       unprocessable_service_plan! unless service_plan_valid?(service_plan, service_instance.space)
+      invalid_service_plan_relation! unless service_plan.service == service_instance.service
     end
 
     service_event_repository = VCAP::CloudController::Repositories::ServiceEventRepository.new(user_audit_info)
@@ -320,4 +321,8 @@ def unprocessable_service_plan!
   def broker_unavailable!
     unprocessable!('The service instance cannot be created because there is an operation in progress for the service broker')
   end
+
+  def invalid_service_plan_relation!
+    raise CloudController::Errors::ApiError.new_from_details('InvalidRelation', 'service plan relates to a different service offering')
+  end
 end

spec/request/service_instances_spec.rb

@@ -1746,6 +1746,37 @@ def check_filtered_instances(*instances)
             )
           end
         end
+
+        context 'service plan is relates to a different service offering' do
+          let!(:service_instance) do
+            VCAP::CloudController::ManagedServiceInstance.make(
+              tags: %w(foo bar),
+              space: space
+            )
+          end
+          let(:guid) { service_instance.guid }
+          let(:plan) { VCAP::CloudController::ServicePlan.make }
+          let(:request_body) do
+            {
+              relationships: {
+                service_plan: {
+                  data: {
+                    guid: plan.guid
+                  }
+                }
+              }
+            }
+          end
+
+          it 'should fail' do
+            api_call.call(admin_headers)
+
+            expect(last_response).to have_status_code(400)
+            expect(parsed_response['errors']).to include(
+              include({ 'detail' => include('service plan relates to a different service offering') })
+            )
+          end
+        end
       end
     end