feat: add sales partner count validation

app/models/form/sales/questions/buyer2_relationship_to_buyer1.rb

@@ -10,7 +10,7 @@ class Form::Sales::Questions::Buyer2RelationshipToBuyer1 < ::Form::Question
   end
 
   ANSWER_OPTIONS = {
-    "P" => { "value" => "Parent" },
+    "P" => { "value" => "Partner" },
     "C" => { "value" => "Child", "hint" => "Must be eligible for child benefit, aged under 16 or under 20 if still in full-time education." },
     "X" => { "value" => "Other" },
     "R" => { "value" => "Buyer prefers not to say" },

app/models/validations/household_validations.rb

@@ -202,10 +202,6 @@ private
     economic_status == 10
   end
 
-  def tenant_is_partner?(relationship)
-    relationship == "P"
-  end
-
   def tenant_is_child?(relationship)
     relationship == "C"
   end

app/models/validations/sales/household_validations.rb

@@ -6,4 +6,11 @@ module Validations::Sales::HouseholdValidations
       record.errors.add :hholdcount, I18n.t("validations.numeric.valid", field: "Number of other people living in the property", min: 0, max: 4)
     end
   end
+
+  def validate_partner_count(record)
+    partner_count = (2..6).count { |n| tenant_is_partner?(record["relat#{n}"]) }
+    if partner_count > 1
+      record.errors.add :base, I18n.t("validations.household.relat.one_partner")
+    end
+  end
 end

app/models/validations/shared_validations.rb

@@ -68,4 +68,8 @@ module Validations::SharedValidations
 
     { scope: status, date: date&.to_formatted_s(:govuk_date), deactivation_date: closest_reactivation&.deactivation_date&.to_formatted_s(:govuk_date) }
   end
+
+  def tenant_is_partner?(relationship)
+    relationship == "P"
+  end
 end