update validation to reflect the fact that an org having no associated rent periods no longer means they accept all rent periods

update tests adding both cases and removing unnecessary additional db additions

app/models/validations/financial_validations.rb

@@ -145,8 +145,9 @@ module Validations::FinancialValidations
   end
 
   def validate_rent_period(record)
-    if record.managing_organisation.present? && record.managing_organisation.rent_periods.present? &&
-        record.period && !record.managing_organisation.rent_periods.include?(record.period)
+    return unless record.managing_organisation && record.period
+
+    unless record.managing_organisation.rent_periods.include? record.period
       record.errors.add :period, :wrong_rent_period, message: I18n.t(
         "validations.financial.rent_period.invalid_for_org",
         org_name: record.managing_organisation.name,

spec/models/validations/financial_validations_spec.rb

@@ -139,23 +139,33 @@ RSpec.describe Validations::FinancialValidations do
   end
 
   describe "rent period validations" do
-    let(:organisation) { FactoryBot.create(:organisation) }
-    let(:user) { FactoryBot.create(:user) }
-    let(:record) { FactoryBot.create(:lettings_log, owning_organisation: user.organisation, managing_organisation: organisation, assigned_to: user) }
+    let(:user) { create(:user) }
+    let(:record) { create(:lettings_log, owning_organisation: user.organisation, managing_organisation: user.organisation, assigned_to: user) }
+    let(:used_period) { 2 }
 
     before do
-      FactoryBot.create(:organisation_relationship, parent_organisation: user.organisation, child_organisation: organisation)
-      FactoryBot.create(:organisation_rent_period, organisation:, rent_period: 2)
+      create(:organisation_rent_period, organisation: user.organisation, rent_period: used_period)
+      record.period = period
     end
 
-    context "when the organisation only uses specific rent periods" do
-      it "validates that the selected rent period is used by the managing organisation" do
-        record.period = 3
+    context "when the log uses a period that the org allows" do
+      let(:period) { used_period }
+
+      it "does not apply a validation" do
+        financial_validator.validate_rent_period(record)
+        expect(record.errors["period"]).to be_empty
+      end
+    end
+
+    context "when the log uses a period that the org does not allow" do
+      let(:period) { used_period + 1 }
+
+      it "does apply a validation" do
         financial_validator.validate_rent_period(record)
         expect(record.errors["period"])
           .to include(match I18n.t(
             "validations.financial.rent_period.invalid_for_org",
-            org_name: organisation.name,
+            org_name: user.organisation.name,
             rent_period: "every 4 weeks",
           ))
       end