Swap Urn class for Application::Urn

This is to avoid the FiberError caused by a multithreaded app server

app/models/application.rb

@@ -60,12 +60,20 @@ def mark_as_qa!
                        unique_by: %i[application_id status])
   end
 
+  after_create :set_urn
+
   validates(:application_date, presence: true)
   validates(:application_route, presence: true)
   validates(:date_of_entry, presence: true)
   validates(:start_date, presence: true)
   validates(:subject, presence: true)
   validates(:visa_type, presence: true)
   validates(:applicant, presence: true)
-  validates(:urn, uniqueness: true)
+  validates(:urn, uniqueness: true, allow_blank: true)
+
+private
+
+  def set_urn
+    update(urn: Urn.new(self).urn) if urn.blank?
+  end
 end

app/services/submit_form.rb

@@ -88,7 +88,6 @@ def create_application
       date_of_entry: form.date_of_entry,
       start_date: form.start_date,
       subject: SubjectStep.new(form).answer.formatted_value,
-      urn: Urn.next(form.application_route),
       visa_type: form.visa_type,
     )
   end

spec/factories/applications.rb

@@ -31,7 +31,6 @@
     visa_type { VisaStep::VALID_ANSWERS_OPTIONS.reject { _1 == "Other" }.sample }
     date_of_entry { Time.zone.today }
     start_date { 1.month.from_now.to_date }
-    urn { Urn.next(application_route) }
 
     factory :teacher_application do
       application_route { "teacher" }

spec/models/application_spec.rb

@@ -67,11 +67,16 @@
   end
 
   describe "#urn" do
-    it "is blank before creation" do
-      application = described_class.new
+    let(:application) { build(:application) }
 
+    it "is blank before creation" do
       expect(application.urn).to be_blank
     end
+
+    it "is set after creation" do
+      application.save
+      expect(application.urn).not_to be_blank
+    end
   end
 
   describe ".search" do

spec/services/submit_form_spec.rb

@@ -126,7 +126,6 @@
             date_of_entry: form.date_of_entry,
             start_date: form.start_date,
             subject: SubjectStep.new(form).answer.formatted_value,
-            urn: kind_of(String),
             visa_type: form.visa_type,
           }
         end
@@ -135,16 +134,11 @@
       end
 
       context "applicant email" do
-        before do
-          allow(Urn).to receive(:next).and_return(urn)
-        end
-
-        let(:urn) { "SOMEURN" }
         let(:expected_email_params) do
           {
             params: {
               email: form.email_address,
-              urn: urn,
+              urn: kind_of(String),
             },
             args: [],
           }