Update model test and answer options

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

@@ -4,13 +4,14 @@ class Form::Sales::Questions::Staircase < ::Form::Question
     @id = "staircase"
     @copy_key = form.start_year_2025_or_later? ? "sales.setup.staircasing" : "sales.sale_information.staircasing"
     @type = "radio"
-    @answer_options = ANSWER_OPTIONS
+    @answer_options = form.start_year_2025_or_later? ? ANSWER_OPTIONS.except("3") : ANSWER_OPTIONS
     @question_number = QUESTION_NUMBER_FROM_YEAR[form.start_date.year] || QUESTION_NUMBER_FROM_YEAR[QUESTION_NUMBER_FROM_YEAR.keys.max]
   end
 
   ANSWER_OPTIONS = {
     "1" => { "value" => "Yes" },
     "2" => { "value" => "No" },
+    "3" => { "value" => "Don’t know" },
   }.freeze
 
   QUESTION_NUMBER_FROM_YEAR = { 2023 => 76, 2024 => 78, 2025 => 7 }.freeze

spec/models/form/sales/questions/staircase_spec.rb

@@ -7,6 +7,10 @@ RSpec.describe Form::Sales::Questions::Staircase, type: :model do
   let(:question_definition) { nil }
   let(:page) { instance_double(Form::Page, subsection: instance_double(Form::Subsection, form: instance_double(Form, start_date: Time.zone.local(2023, 4, 1)))) }
 
+  before do
+    allow(page.subsection.form).to receive(:start_year_2025_or_later?).and_return(false)
+  end
+
   it "has correct page" do
     expect(question.page).to eq(page)
   end