Disallow to modify the start date for an already started poll

We need to update a couple of tests because a poll is created in the
tests with a timestamp that includes nanoseconds and in the form to edit
the time of the poll the nanoseconds are not sent, meaning it was
detected as a change.

app/models/poll.rb

@@ -152,10 +152,14 @@ class Poll < ApplicationRecord
   end
 
   def start_date_change
-    if will_save_change_to_starts_at? && starts_at < Time.current
+    if will_save_change_to_starts_at?
+      if starts_at_in_database < Time.current
+        errors.add(:starts_at, I18n.t("errors.messages.cannot_change_date.poll_started"))
+      elsif starts_at < Time.current
         errors.add(:starts_at, I18n.t("errors.messages.past_date"))
       end
     end
+  end
 
   def generate_slug?
     slug.nil?

config/locales/en/general.yml

@@ -138,6 +138,8 @@ en:
       user_not_found: User not found
       invalid_date_range: "Invalid date range"
       past_date: "Must not be a past date"
+      cannot_change_date:
+        poll_started: "Cannot be changed if voting has already started"
   form:
     accept_terms: I agree to the %{policy} and the %{conditions}
     accept_terms_title: I agree to the Privacy Policy and the Terms and conditions of use

config/locales/es/general.yml

@@ -138,6 +138,8 @@ es:
       user_not_found: Usuario no encontrado
       invalid_date_range: "El rango de fechas no es válido"
       past_date: "No puede ser una fecha pasada"
+      cannot_change_date:
+        poll_started: "No puede ser cambiada si la votación ha comenzado"
   form:
     accept_terms: Acepto la %{policy} y las %{conditions}
     accept_terms_title: Acepto la Política de privacidad y las Condiciones de uso

spec/models/poll/poll_spec.rb

@@ -62,6 +62,13 @@ describe Poll do
         poll.starts_at = 1.minute.ago
         expect(poll).not_to be_valid
       end
+
+      it "is not valid if changing the start date for an already started poll" do
+        poll = create(:poll, starts_at: 10.days.ago)
+
+        poll.starts_at = 10.days.from_now
+        expect(poll).not_to be_valid
+      end
     end
   end
 

spec/system/admin/poll/polls_spec.rb

@@ -553,7 +553,7 @@ describe "Admin polls", :admin do
     end
 
     scenario "edit poll with sdg related list" do
-      poll = create(:poll, name: "Upcoming poll with SDG related content")
+      poll = create(:poll, :future, name: "Upcoming poll with SDG related content")
       poll.sdg_goals = [SDG::Goal[1], SDG::Goal[17]]
       visit edit_admin_poll_path(poll)
 

spec/system/admin/translatable_spec.rb

@@ -242,7 +242,7 @@ describe "Admin edit translatable records", :admin do
     end
 
     context "Change value of a translated field to blank" do
-      let(:translatable) { create(:poll) }
+      let(:translatable) { create(:poll, :future) }
       let(:path) { edit_admin_poll_path(translatable) }
 
       scenario "Updates the field to a blank value" do