write helper method to support having the correct rent period checkboxes checked

app/helpers/organisations_helper.rb

@@ -37,4 +37,14 @@ module OrganisationsHelper
       end
     end
   end
+
+  def rent_periods_with_checked_attr(checked_periods: nil)
+    all_rent_periods = RentPeriod.rent_period_mappings
+    rent_periods = all_rent_periods.map do |code, period|
+      period_copy = period.clone
+      period_copy[:checked] = true if checked_periods.nil? || checked_periods.include?(code)
+      [code, period_copy]
+    end
+    rent_periods.to_h
+  end
 end

spec/helpers/organisations_helper_spec.rb

@@ -20,4 +20,39 @@ RSpec.describe OrganisationsHelper do
       )
     end
   end
+
+  describe "rent_periods_with_checked_attr" do
+    let(:fake_rent_periods) do
+      {
+        "1" => { "value" => "Every minute" },
+        "2" => { "value" => "Every decade" },
+      }
+    end
+
+    before do
+      allow(RentPeriod).to receive(:rent_period_mappings).and_return fake_rent_periods
+    end
+
+    it "returns rent_period_mappings" do
+      actual = rent_periods_with_checked_attr
+      expect(actual.keys).to eq RentPeriod.rent_period_mappings.keys
+    end
+
+    context "when checked_periods is nil" do
+      it "returns all rent periods with checked true" do
+        actual = rent_periods_with_checked_attr
+        checked_attrs = actual.values.map { |p| p[:checked] }
+        expect(checked_attrs).to all be true
+      end
+    end
+
+    context "when checked_periods is not nil" do
+      it "returns the rent_periods with the correct values checked" do
+        checked_rent_period = "1"
+        actual = rent_periods_with_checked_attr(checked_periods: [checked_rent_period])
+        expect(actual[checked_rent_period][:checked]).to be true
+        expect(actual["2"][:checked]).to be_falsey
+      end
+    end
+  end
 end