CLDC-4146 infer no other partners (#3152)

* CLDC-4146 infer no to multiple partners

* CLDC-4146 try removing factory change

* Simplify inference logic

* Fix not equals logic

* Improve person_partner tests

* Add tests for new not equals logic

* Improve person_lead_partner tests

* Fix inference logic

* Revert to simpler inference logic

* Correct hidden_in_check_answers logic

* Fixed derived?

* Improve lettings log variables tests

* Pull out resetting partner fields into method

* Convert 'else next' to guard clause

* Refactor infer_only_partner!

* Match updated requirements

* Fix tests

* Small tweaks

* Remove redundant logic from infer_at_most_one_relationship!

* Remove redundant `disable_clearing_if_not_routed_or_dynamic_answer_options`

* Add tests for question number

* Remove puts

* Refactor derived fields tests

* Fix lint

* After build, set nil values for `details_known` to 0

* Add details_known to tests

* Add question mark to method name

* Rewrite `is_another_person_partner?` to be `is_any_person_partner?`

* Move skip in form flow method from page to question

* Fix tests

* Fix tests after merge

---------

Co-authored-by: Carolyn <carolyn.barker@softwire.com>
Co-authored-by: oscar-richardson-softwire <oscar.richardson@softwire.com>

app/models/derived_variables/lettings_log_variables.rb

@@ -75,6 +75,10 @@ module DerivedVariables::LettingsLogVariables
       self.beds = nil
     end
 
+    if form.start_year_2026_or_later?
+      infer_at_most_one_relationship!
+    end
+
     clear_child_constraints_for_age_changes!
     child_under_16_constraints!
 
@@ -325,6 +329,25 @@ private
     end
   end
 
+  def infer_at_most_one_relationship!
+    new_partner_numbers = partner_numbers.select { |i| public_send("relat#{i}_changed?") }
+    return unless new_partner_numbers.any?
+
+    infer_only_partner!(new_partner_numbers.first)
+  end
+
+  def infer_only_partner!(partner_number)
+    return unless hhmemb
+
+    (2..hhmemb).each do |i|
+      next if i == partner_number
+
+      if ["P", nil].include?(public_send("relat#{i}"))
+        self["relat#{i}"] = "X"
+      end
+    end
+  end
+
   def household_type
     return unless totelder && totadult && totchild
 

app/models/form.rb

@@ -108,7 +108,8 @@ class Form
 
     return :check_answers if next_page.nil?
     return next_page.id if next_page.routed_to?(log, current_user) &&
-      (!ignore_answered || next_page.has_unanswered_questions?(log))
+      (!ignore_answered || next_page.has_unanswered_questions?(log)) &&
+      next_page.questions.any? { |question| !question.skip_question_in_form_flow?(log) }
 
     next_page_id(next_page, log, current_user, ignore_answered:)
   end
@@ -323,7 +324,12 @@ class Form
         if value.is_a?(Hash) && value.key?("operator")
           operator = value["operator"]
           operand = value["operand"]
-          log[question]&.send(operator, operand)
+
+          if operator == "!=" # This branch is needed as `nil` does not behave as expected with the default logic (`nil&.send("!=", nil)` => `nil` i.e., `false`).
+            log[question] != operand
+          else
+            log[question]&.send(operator, operand)
+          end
         else
           parts = question.split(".")
           log_value = send_chain(parts, log)

app/models/form/lettings/pages/person_lead_partner.rb

@@ -19,7 +19,10 @@ class Form::Lettings::Pages::PersonLeadPartner < ::Form::Page
             "operand" => 16,
           },
         },
-        { "details_known_#{@person_index}" => 0, "age#{@person_index}" => nil },
+        {
+          "details_known_#{@person_index}" => 0,
+          "age#{@person_index}" => nil,
+        },
       ]
     else
       [{ "details_known_#{@person_index}" => 0 }]

app/models/form/lettings/questions/person_partner.rb

@@ -35,6 +35,10 @@ class Form::Lettings::Questions::PersonPartner < ::Form::Question
   end
 
   def derived?(log)
-    form.start_year_2026_or_later? && log.is_partner_inferred?(@person_index)
+    form.start_year_2026_or_later? && log.is_person_under_16?(@person_index)
+  end
+
+  def skip_question_in_form_flow?(log)
+    form.start_year_2026_or_later? && log.is_any_person_partner?
   end
 end

app/models/form/lettings/subsections/household_characteristics.rb

@@ -52,15 +52,15 @@ class Form::Lettings::Subsections::HouseholdCharacteristics < ::Form::Subsection
       Form::Lettings::Pages::PersonKnown.new(nil, nil, self, person_index:),
       (Form::Lettings::Pages::PersonAge.new(nil, nil, self, person_index:) if form.start_year_2026_or_later?),
       relationship_question(person_index:),
-      (Form::Lettings::Pages::PartnerUnder16ValueCheck.new("relationship_#{person_index}_partner_under_16_value_check", nil, self, person_index:) if form.start_year_2024_or_later? && !form.start_year_2026_or_later?),
-      (Form::Lettings::Pages::MultiplePartnersValueCheck.new("relationship_#{person_index}_multiple_partners_value_check", nil, self, person_index:) if form.start_year_2024_or_later?),
+      (Form::Lettings::Pages::PartnerUnder16ValueCheck.new("relationship_#{person_index}_partner_under_16_value_check", nil, self, person_index:) unless form.start_year_2026_or_later?),
+      (Form::Lettings::Pages::MultiplePartnersValueCheck.new("relationship_#{person_index}_multiple_partners_value_check", nil, self, person_index:) unless form.start_year_2026_or_later?),
       (Form::Lettings::Pages::PersonAge.new(nil, nil, self, person_index:) unless form.start_year_2026_or_later?),
       (Form::Lettings::Pages::NoFemalesPregnantHouseholdPersonAgeValueCheck.new(nil, nil, self, person_index:) unless form.start_year_2026_or_later?),
       (Form::Lettings::Pages::FemalesInSoftAgeRangeInPregnantHouseholdPersonAgeValueCheck.new(nil, nil, self, person_index:) unless form.start_year_2026_or_later?),
       (Form::Lettings::Pages::NoHouseholdMemberLikelyToBePregnantCheck.new("no_household_member_likely_to_be_pregnant_person_age_#{person_index}_check", nil, self, person_index:) if form.start_year_2026_or_later?),
       Form::Lettings::Pages::PersonUnderRetirementValueCheck.new("age_#{person_index}_under_retirement_value_check", nil, self, person_index:),
       Form::Lettings::Pages::PersonOverRetirementValueCheck.new("age_#{person_index}_over_retirement_value_check", nil, self, person_index:),
-      (Form::Lettings::Pages::PartnerUnder16ValueCheck.new("age_#{person_index}_partner_under_16_value_check", nil, self, person_index:) if form.start_year_2024_or_later? && !form.start_year_2026_or_later?),
+      (Form::Lettings::Pages::PartnerUnder16ValueCheck.new("age_#{person_index}_partner_under_16_value_check", nil, self, person_index:) unless form.start_year_2026_or_later?),
       (Form::Lettings::Pages::PersonSexRegisteredAtBirth.new(nil, nil, self, person_index:) if form.start_year_2026_or_later?),
       (Form::Lettings::Pages::PersonGenderSameAsSex.new(nil, nil, self, person_index:) if form.start_year_2026_or_later?),
       (Form::Lettings::Pages::PersonGenderIdentity.new(nil, nil, self, person_index:) unless form.start_year_2026_or_later?),

app/models/form/question.rb

@@ -304,6 +304,10 @@ class Form::Question
     nil
   end
 
+  def skip_question_in_form_flow?(_log)
+    false
+  end
+
 private
 
   def selected_answer_option_is_derived?(log)

app/models/lettings_log.rb

@@ -445,10 +445,14 @@ class LettingsLog < Log
     unittype_gn_changed? && unittype_gn_was == 2
   end
 
-  def is_partner_inferred?(person_index)
+  def is_person_under_16?(person_index)
     public_send("age#{person_index}") && public_send("age#{person_index}") < 16
   end
 
+  def is_any_person_partner?
+    !partner_numbers.empty?
+  end
+
   def age_changed_from_below_16(person_index)
     public_send("age#{person_index}_was") && public_send("age#{person_index}_was") < 16
   end
@@ -943,6 +947,10 @@ private
     end
   end
 
+  def partner_numbers
+    (2..8).select { |i| public_send("relat#{i}") == "P" }
+  end
+
   def age_refused?
     [age1_known, age2_known, age3_known, age4_known, age5_known, age6_known, age7_known, age8_known].any?(1)
   end

spec/features/form/page_routing_spec.rb

@@ -270,6 +270,78 @@ RSpec.describe "Form Page Routing" do
 
         expect(lettings_log.form.depends_on_met(depends_on, lettings_log)).to be(true)
       end
+
+      describe "using the 'not equal to' operator" do
+        it "returns true if both values are non-nil and different" do
+          depends_on = [
+            {
+              "relat2" => {
+                "operator" => "!=",
+                "operand" => "P",
+              },
+            },
+          ]
+          lettings_log.relat2 = "X"
+
+          expect(lettings_log.form.depends_on_met(depends_on, lettings_log)).to be(true)
+        end
+
+        it "returns false if both values are non-nil and the same" do
+          depends_on = [
+            {
+              "relat2" => {
+                "operator" => "!=",
+                "operand" => "P",
+              },
+            },
+          ]
+          lettings_log.relat2 = "P"
+
+          expect(lettings_log.form.depends_on_met(depends_on, lettings_log)).to be(false)
+        end
+
+        it "returns true if the being tested is nil and the operand is non-nil" do
+          depends_on = [
+            {
+              "relat2" => {
+                "operator" => "!=",
+                "operand" => "P",
+              },
+            },
+          ]
+          lettings_log.relat2 = nil
+
+          expect(lettings_log.form.depends_on_met(depends_on, lettings_log)).to be(true)
+        end
+
+        it "returns true if the being tested is non-nil and the operand is nil" do
+          depends_on = [
+            {
+              "relat2" => {
+                "operator" => "!=",
+                "operand" => nil,
+              },
+            },
+          ]
+          lettings_log.relat2 = "P"
+
+          expect(lettings_log.form.depends_on_met(depends_on, lettings_log)).to be(true)
+        end
+
+        it "returns false if both values are nil" do
+          depends_on = [
+            {
+              "relat2" => {
+                "operator" => "!=",
+                "operand" => nil,
+              },
+            },
+          ]
+          lettings_log.relat2 = nil
+
+          expect(lettings_log.form.depends_on_met(depends_on, lettings_log)).to be(false)
+        end
+      end
     end
   end
 

spec/models/form/lettings/pages/person_lead_partner_spec.rb

@@ -28,8 +28,6 @@ RSpec.describe Form::Lettings::Pages::PersonLeadPartner, type: :model do
     end
 
     context "with start year < 2026", metadata: { year: 25 } do
-      let(:person_question_count) { 4 }
-
       it "has correct depends_on" do
         expect(page.depends_on).to eq(
           [{ "details_known_2" => 0 }],
@@ -39,7 +37,6 @@ RSpec.describe Form::Lettings::Pages::PersonLeadPartner, type: :model do
 
     context "with start year >= 2026", metadata: { year: 26 } do
       let(:start_year_2026_or_later?) { true }
-      let(:person_question_count) { 5 }
 
       it "has correct depends_on" do
         expect(page.depends_on).to eq(
@@ -70,8 +67,6 @@ RSpec.describe Form::Lettings::Pages::PersonLeadPartner, type: :model do
     end
 
     context "with start year < 2026", metadata: { year: 25 } do
-      let(:person_question_count) { 4 }
-
       it "has correct depends_on" do
         expect(page.depends_on).to eq(
           [{ "details_known_3" => 0 }],
@@ -81,7 +76,6 @@ RSpec.describe Form::Lettings::Pages::PersonLeadPartner, type: :model do
 
     context "with start year >= 2026", metadata: { year: 26 } do
       let(:start_year_2026_or_later?) { true }
-      let(:person_question_count) { 5 }
 
       it "has correct depends_on" do
         expect(page.depends_on).to eq(

spec/models/form/lettings/questions/person_partner_spec.rb

@@ -24,6 +24,8 @@ RSpec.describe Form::Lettings::Questions::PersonPartner, type: :model do
     )
   end
   let(:person_index) { 2 }
+  let(:is_any_person_partner?) { false }
+  let(:log) { instance_double(LettingsLog, is_any_person_partner?: is_any_person_partner?) }
 
   it "has correct page" do
     expect(question.page).to eq(page)
@@ -47,6 +49,48 @@ RSpec.describe Form::Lettings::Questions::PersonPartner, type: :model do
     expect(question.hidden_in_check_answers).to be_nil
   end
 
+  describe "#skip_page_in_form_flow?" do
+    context "with start year < 2026", metadata: { year: 25 } do
+      let(:year) { 2025 }
+
+      context "when no other person is the partner of the lead tenant" do
+        let(:is_any_person_partner?) { false }
+
+        it "returns false" do
+          expect(question.skip_question_in_form_flow?(log)).to be false
+        end
+      end
+
+      context "when another person is the partner of the lead tenant" do
+        let(:is_any_person_partner?) { true }
+
+        it "returns false" do
+          expect(question.skip_question_in_form_flow?(log)).to be false
+        end
+      end
+    end
+
+    context "with start year >= 2026", metadata: { year: 26 } do
+      let(:year) { 2026 }
+
+      context "when no other person is the partner of the lead tenant" do
+        let(:is_any_person_partner?) { false }
+
+        it "returns false" do
+          expect(question.skip_question_in_form_flow?(log)).to be false
+        end
+      end
+
+      context "when another person is the partner of the lead tenant" do
+        let(:is_any_person_partner?) { true }
+
+        it "returns true" do
+          expect(question.skip_question_in_form_flow?(log)).to be true
+        end
+      end
+    end
+  end
+
   context "with person 2" do
     it "has the correct id" do
       expect(question.id).to eq("relat2")
@@ -56,39 +100,49 @@ RSpec.describe Form::Lettings::Questions::PersonPartner, type: :model do
       expect(question.check_answers_card_number).to eq(2)
     end
 
-    context "with person 2 age < 16" do
-      let(:log) { build(:lettings_log, age2: 10) }
+    context "and in 2025", metadata: { year: 25 } do
+      let(:year) { 2025 }
+      let(:person_question_count) { 4 }
 
-      context "and in 2025", metadata: { year: 25 } do
-        let(:year) { 2025 }
+      it "has the correct question number" do
+        expect(question.question_number).to eq(37)
+      end
+
+      context "with person 2 age < 16" do
+        let(:log) { build(:lettings_log, age2: 10) }
 
         it "is not marked as derived" do
           expect(question.derived?(log)).to be false
         end
       end
 
-      context "and in 2026", metadata: { year: 26 } do
-        let(:year) { 2026 }
+      context "with person 2 age >= 16" do
+        let(:log) { build(:lettings_log, age2: 20) }
 
-        it "is marked as derived" do
-          expect(question.derived?(log)).to be true
+        it "is not marked as derived" do
+          expect(question.derived?(log)).to be false
         end
       end
     end
 
-    context "with person 2 age >= 16" do
-      let(:log) { build(:lettings_log, age2: 20) }
+    context "and in 2026", metadata: { year: 26 } do
+      let(:year) { 2026 }
+      let(:person_question_count) { 5 }
 
-      context "and in 2025", metadata: { year: 25 } do
-        let(:year) { 2025 }
+      it "has the correct question number" do
+        expect(question.question_number).to eq(38)
+      end
 
-        it "is not marked as derived" do
-          expect(question.derived?(log)).to be false
+      context "with person 2 age < 16" do
+        let(:log) { build(:lettings_log, age2: 10) }
+
+        it "is marked as derived" do
+          expect(question.derived?(log)).to be true
         end
       end
 
-      context "and in 2026", metadata: { year: 26 } do
-        let(:year) { 2026 }
+      context "with person 2 age >= 16" do
+        let(:log) { build(:lettings_log, age2: 20) }
 
         it "is not marked as derived" do
           expect(question.derived?(log)).to be false

spec/models/form/lettings/subsections/household_characteristics_spec.rb

@@ -357,7 +357,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_2_known
           person_2_age
           person_2_lead_partner
-          relationship_2_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_2_check
           age_2_under_retirement_value_check
           age_2_over_retirement_value_check
@@ -372,7 +371,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_3_known
           person_3_age
           person_3_lead_partner
-          relationship_3_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_3_check
           age_3_under_retirement_value_check
           age_3_over_retirement_value_check
@@ -387,7 +385,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_4_known
           person_4_age
           person_4_lead_partner
-          relationship_4_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_4_check
           age_4_under_retirement_value_check
           age_4_over_retirement_value_check
@@ -402,7 +399,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_5_known
           person_5_age
           person_5_lead_partner
-          relationship_5_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_5_check
           age_5_under_retirement_value_check
           age_5_over_retirement_value_check
@@ -417,7 +413,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_6_known
           person_6_age
           person_6_lead_partner
-          relationship_6_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_6_check
           age_6_under_retirement_value_check
           age_6_over_retirement_value_check
@@ -432,7 +427,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_7_known
           person_7_age
           person_7_lead_partner
-          relationship_7_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_7_check
           age_7_under_retirement_value_check
           age_7_over_retirement_value_check
@@ -447,7 +441,6 @@ RSpec.describe Form::Lettings::Subsections::HouseholdCharacteristics, type: :mod
           person_8_known
           person_8_age
           person_8_lead_partner
-          relationship_8_multiple_partners_value_check
           no_household_member_likely_to_be_pregnant_person_age_8_check
           age_8_under_retirement_value_check
           age_8_over_retirement_value_check

spec/models/form_spec.rb

@@ -19,10 +19,45 @@ RSpec.describe Form, type: :model do
     let(:previous_page_id) { form.get_page("person_1_age") }
     let(:value_check_previous_page) { form.get_page("net_income_value_check") }
 
-    it "returns the next page given the previous" do
+    it "returns the next page, given the previous" do
       expect(form.next_page_id(previous_page_id, lettings_log, user)).to eq("person_1_gender")
     end
 
+    context "when the next page has more than one question" do
+      let(:previous_page_id) { form.get_page("tenancy_start_date") }
+      let(:next_page) { form.get_page("rent_type") }
+
+      context "when every question on the next page returns `true` from its `skip_question_in_form_flow?` method" do
+        before do
+          allow(next_page.questions.first).to receive(:skip_question_in_form_flow?)
+            .with(lettings_log)
+            .and_return(true)
+          allow(next_page.questions.second).to receive(:skip_question_in_form_flow?)
+            .with(lettings_log)
+            .and_return(true)
+        end
+
+        it "returns the page after next, given the previous" do
+          expect(form.next_page_id(previous_page_id, lettings_log, user)).to eq("tenant_code")
+        end
+      end
+
+      context "when at least question on the next page returns `false` from its `skip_question_in_form_flow?` method" do
+        before do
+          allow(next_page.questions.first).to receive(:skip_question_in_form_flow?)
+            .with(lettings_log)
+            .and_return(true)
+          allow(next_page.questions.second).to receive(:skip_question_in_form_flow?)
+            .with(lettings_log)
+            .and_return(false)
+        end
+
+        it "returns the next page, given the previous" do
+          expect(form.next_page_id(previous_page_id, lettings_log, user)).to eq("rent_type")
+        end
+      end
+    end
+
     context "when the current page is a value check page" do
       before do
         lettings_log.hhmemb = 1

spec/models/lettings_log_derived_fields_spec.rb

@@ -1588,4 +1588,323 @@ RSpec.describe LettingsLog, type: :model do
       end
     end
   end
+
+  describe "#infer_at_most_one_relationship!" do
+    context "when 2025", metadata: { year: 25 } do
+      before do
+        Timecop.freeze(collection_start_date_for_year(2025))
+        Singleton.__init__(FormHandler)
+      end
+
+      after do
+        Timecop.return
+        Singleton.__init__(FormHandler)
+      end
+
+      context "when there are no existing relationships" do
+        let(:log) { create(:lettings_log, :in_progress, hhmemb: 6, details_known_2: 0, details_known_3: 0, details_known_4: 0, details_known_5: 0, details_known_6: 0, relat2: nil, relat3: "X", relat4: "X", relat5: "R") }
+
+        context "when a new relationship is added" do
+          before do
+            log.relat4 = "P"
+          end
+
+          it "does not infer no to any relationship answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+      end
+
+      context "when there is an existing relationship" do
+        let(:log) { create(:lettings_log, :in_progress, hhmemb: 6, details_known_2: 0, details_known_3: 0, details_known_4: 0, details_known_5: 0, details_known_6: 0, relat2: "X", relat3: "P", relat4: "R", relat5: "X") }
+
+        context "when a new relationship is added" do
+          before do
+            log.relat2 = "P"
+          end
+
+          it "does not infer no to any relationship answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+
+        context "when the relationship is removed" do
+          before do
+            log.relat3 = "X"
+          end
+
+          it "does not reset any answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+      end
+
+      context "when more than one relationship is set" do
+        let(:log) { create(:lettings_log, :in_progress, hhmemb: 6, details_known_2: 0, details_known_3: 0, details_known_4: 0, details_known_5: 0, details_known_6: 0, relat2: "X", relat3: "X", relat4: "R", relat5: "X") }
+
+        before do
+          log.relat2 = "P"
+          log.relat3 = "P"
+        end
+
+        it "does not infer no to any relationship answers" do
+          expect { log.set_derived_fields! }
+            .to not_change(log, :relat2)
+            .and not_change(log, :relat3)
+            .and not_change(log, :relat4)
+            .and not_change(log, :relat5)
+            .and not_change(log, :relat6)
+            .and not_change(log, :relat7)
+            .and not_change(log, :relat8)
+        end
+      end
+    end
+
+    context "when 2026", metadata: { year: 26 } do
+      before do
+        Timecop.freeze(collection_start_date_for_year(2026))
+        Singleton.__init__(FormHandler)
+      end
+
+      after do
+        Timecop.return
+        Singleton.__init__(FormHandler)
+      end
+
+      context "when there are no existing relationships" do
+        let(:log) { create(:lettings_log, :in_progress, hhmemb: 6, details_known_2: 0, details_known_3: 0, details_known_4: 0, details_known_5: 0, details_known_6: 0, relat3: "X", relat4: "X", relat5: "R") }
+
+        context "when a new relationship is added" do
+          before do
+            log.relat4 = "P"
+          end
+
+          it "infers no to unanswered questions" do
+            expect { log.set_derived_fields! }
+              .to change(log, :relat2).to("X")
+              .and change(log, :relat6).to("X")
+          end
+
+          it "does not change relationship answers for people not in the household" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+
+          it "does not change relationship answers of no or prefer not to say" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat3)
+              .and not_change(log, :relat5)
+          end
+
+          it "does not change the relationship answer for the newly added relationship" do
+            expect { log.set_derived_fields! }.to not_change(log, :relat4)
+          end
+        end
+
+        context "when a 'no' is changed to 'prefers not to say'" do
+          before do
+            log.relat4 = "R"
+          end
+
+          it "does not change any relationship answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+
+        context "when a 'prefers not to say' is changed to 'no'" do
+          before do
+            log.relat5 = "X"
+          end
+
+          it "does not change any relationship answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+      end
+
+      context "when there is an existing relationship" do
+        let(:log) { create(:lettings_log, :in_progress, hhmemb: 6, details_known_2: 0, details_known_3: 0, details_known_4: 0, details_known_5: 0, details_known_6: 0, relat2: "X", relat3: "P", relat4: "R", relat5: "X") }
+
+        context "and a new relationship is added to an earlier person than the existing one" do
+          before do
+            log.relat6 = nil # This is necessary because `log.set_derived_fields!` runs when the log is created from the factory, which sets `relat6` to "X".
+            log.relat2 = "P"
+          end
+
+          it "infers no to the existing relationship" do
+            expect { log.set_derived_fields! }.to change(log, :relat3).to "X"
+          end
+
+          it "infers no to unanswered questions" do
+            expect { log.set_derived_fields! }.to change(log, :relat6).to "X"
+          end
+
+          it "does not change relationship answers for people not in the household" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+
+          it "does not change relationship answers of no or prefer not to say" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat5)
+              .and not_change(log, :relat4)
+          end
+
+          it "does not change the relationship answer for the newly added relationship" do
+            expect { log.set_derived_fields! }.to not_change(log, :relat2)
+          end
+        end
+
+        context "and a new relationship is added to an later person than the existing one" do
+          before do
+            log.relat6 = nil # This is necessary because `log.set_derived_fields!` runs when the log is created from the factory, which sets `relat6` to "X".
+            log.relat5 = "P"
+          end
+
+          it "infers no to the existing relationship" do
+            expect { log.set_derived_fields! }.to change(log, :relat3).to "X"
+          end
+
+          it "infers no to unanswered questions" do
+            expect { log.set_derived_fields! }.to change(log, :relat6).to "X"
+          end
+
+          it "does not change relationship answers for people not in the household" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+
+          it "does not change relationship answers of no or prefer not to say" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat4)
+          end
+
+          it "does not change the relationship answer for the newly added relationship" do
+            expect { log.set_derived_fields! }.to not_change(log, :relat5)
+          end
+        end
+
+        context "when a 'no' is changed to 'prefers not to say'" do
+          before do
+            log.relat4 = "R"
+          end
+
+          it "does not change any relationship answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+
+        context "when a 'prefers not to say' is changed to 'no'" do
+          before do
+            log.relat5 = "X"
+          end
+
+          it "does not change any relationship answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+
+        context "and the relationship is removed" do
+          before do
+            log.relat3 = "X"
+          end
+
+          it "does not reset any answers" do
+            expect { log.set_derived_fields! }
+              .to not_change(log, :relat2)
+              .and not_change(log, :relat3)
+              .and not_change(log, :relat4)
+              .and not_change(log, :relat5)
+              .and not_change(log, :relat6)
+              .and not_change(log, :relat7)
+              .and not_change(log, :relat8)
+          end
+        end
+      end
+
+      context "when more than one relationship is set" do
+        let(:log) { create(:lettings_log, :in_progress, hhmemb: 6, details_known_2: 0, details_known_3: 0, details_known_4: 0, details_known_5: 0, details_known_6: 0, relat2: "X", relat3: "X", relat4: "R", relat5: "X") }
+
+        before do
+          log.relat2 = "P"
+          log.relat3 = "P"
+        end
+
+        it "keeps the lower numbered relationship and infers the higher numbered one to false" do
+          expect { log.set_derived_fields! }
+            .to not_change(log, :relat2)
+            .and change(log, :relat3).to("X")
+        end
+
+        it "infers no to unanswered questions" do
+          expect { log.set_derived_fields! }.to change(log, :relat6).to "X"
+        end
+
+        it "does not change relationship answers for people not in the household" do
+          expect { log.set_derived_fields! }
+            .to not_change(log, :relat7)
+            .and not_change(log, :relat8)
+        end
+
+        it "does not change relationship answers of no or prefer not to say" do
+          expect { log.set_derived_fields! }
+            .to not_change(log, :relat5)
+            .and not_change(log, :relat4)
+        end
+      end
+    end
+  end
 end

spec/models/lettings_log_spec.rb

@@ -2349,5 +2349,23 @@ RSpec.describe LettingsLog do
       end
     end
   end
+
+  describe "#is_any_person_partner?" do
+    context "when no person is the partner of the lead tenant" do
+      let(:log) { create(:lettings_log, :in_progress, hhmemb: 3, details_known_2: 0, details_known_3: 0, relat2: "X", relat3: "R") }
+
+      it "returns false" do
+        expect(log.is_any_person_partner?).to be false
+      end
+    end
+
+    context "when a person is the partner of the lead tenant" do
+      let(:log) { create(:lettings_log, :in_progress, hhmemb: 3, details_known_2: 0, details_known_3: 0, relat2: "X", relat3: "P") }
+
+      it "returns true" do
+        expect(log.is_any_person_partner?).to be true
+      end
+    end
+  end
 end
 # rubocop:enable RSpec/MessageChain