validate sales log head count between 0 and 4

app/models/sales_log.rb

@@ -1,5 +1,10 @@
 class SalesLogValidator < ActiveModel::Validator
-  def validate(record); end
+  include Validations::Sales::HouseholdValidations
+
+  def validate(record)
+    validation_methods = public_methods.select { |method| method.starts_with?("validate_") }
+    validation_methods.each { |meth| public_send(meth, record) }
+  end
 end
 
 class SalesLog < Log

app/models/validations/sales/household_validations.rb

@@ -0,0 +1,9 @@
+module Validations::Sales::HouseholdValidations
+  def validate_number_of_other_people_living_in_the_property(record)
+    return if record.hholdcount.blank?
+
+    unless record.hholdcount >= 0 && record.hholdcount <= 4
+      record.errors.add :hholdcount, I18n.t("validations.numeric.valid", field: "Number of other people living in the property", min: 0, max: 4)
+    end
+  end
+end

spec/models/validations/sales/household_validations_spec.rb

@@ -0,0 +1,49 @@
+require "rails_helper"
+
+RSpec.describe Validations::Sales::HouseholdValidations do
+  subject(:household_validator) { validator_class.new }
+
+  let(:validator_class) { Class.new { include Validations::Sales::HouseholdValidations } }
+
+  describe "#validate_number_of_other_people_living_in_the_property" do
+    context "when within permitted bounds" do
+      let(:record) { FactoryBot.build(:sales_log, hholdcount: 2) }
+
+      it "does not add an error" do
+        household_validator.validate_number_of_other_people_living_in_the_property(record)
+
+        expect(record.errors).not_to be_present
+      end
+    end
+
+    context "when blank" do
+      let(:record) { FactoryBot.build(:sales_log, hholdcount: nil) }
+
+      it "does not add an error" do
+        household_validator.validate_number_of_other_people_living_in_the_property(record)
+
+        expect(record.errors).not_to be_present
+      end
+    end
+
+    context "when below lower bound" do
+      let(:record) { FactoryBot.build(:sales_log, hholdcount: -1) }
+
+      it "adds an error" do
+        household_validator.validate_number_of_other_people_living_in_the_property(record)
+
+        expect(record.errors).to be_present
+      end
+    end
+
+    context "when higher than upper bound" do
+      let(:record) { FactoryBot.build(:sales_log, hholdcount: 5) }
+
+      it "adds an error" do
+        household_validator.validate_number_of_other_people_living_in_the_property(record)
+
+        expect(record.errors).to be_present
+      end
+    end
+  end
+end