add joint tenancy validation

app/models/validations/tenancy_validations.rb

@@ -32,4 +32,10 @@ module Validations::TenancyValidations
   def validate_other_tenancy_type(record)
     validate_other_field(record, 3, :tenancy, :tenancyother)
   end
+
+  def validate_joint_tenancy(record)
+    if record.hhmemb == 1 && record.joint != 2
+      record.errors.add :joint, I18n.t("validations.tenancy.not_joint")
+    end
+  end
 end

config/locales/en.yml

@@ -221,6 +221,7 @@ en:
         secure: "Secure (including flexible) should be between 2 and 99 years or not specified"
       internal_transfer: "Answer must be secure tenancy as you already told us this tenancy is an internal transfer"
       cannot_be_internal_transfer: "Answer cannot be internal transfer as you already told us this is not a secure tenancy"
+      not_joint: "This cannot be a joint tenancy as you've told us there's only one person in the household"
 
     declaration:
       missing: "You must show the DLUHC privacy notice to the tenant before you can submit this log."

spec/models/validations/tenancy_validations_spec.rb

@@ -146,4 +146,24 @@ RSpec.describe Validations::TenancyValidations do
       end
     end
   end
+
+  describe "joint tenancy validation" do
+    context "when the data inputter has said that there is only one member in the household" do
+      let(:expected_error) { I18n.t("validations.tenancy.not_joint") }
+
+      it "displays an error if the data inputter says the letting is a joint tenancy" do
+        record.hhmemb = 1
+        record.joint = 1
+        tenancy_validator.validate_joint_tenancy(record)
+        expect(record.errors["joint"]).to include(match(expected_error))
+      end
+
+      it "does not display an error if the data inputter says the letting is not a joint tenancy" do
+        record.hhmemb = 1
+        record.joint = 2
+        tenancy_validator.validate_joint_tenancy(record)
+        expect(record.errors["joint"]).to be_empty
+      end
+    end
+  end
 end