Added a spec file in order to test the tax categories helper

spec/helpers/spree/admin/tax_categories_helper_spec.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe Spree::Admin::TaxCategoriesHelper do
+  describe '#tax_category_dropdown_options' do
+    let!(:default_tax_category) { create(:tax_category, is_default: true) }
+    let!(:other_tax_category) { create(:tax_category, is_default: false) }
+
+    context 'when products require a tax category' do
+      it 'returns include_blank as false' do
+        options = helper.tax_category_dropdown_options(true)
+        expect(options[:include_blank]).to eq(false)
+      end
+
+      it 'returns the default tax category as selected' do
+        options = helper.tax_category_dropdown_options(true)
+        expect(options[:selected]).to eq(default_tax_category.id)
+      end
+
+      context 'when no default tax category exists' do
+        before { default_tax_category.update(is_default: false) }
+
+        it 'returns nil for the selected value' do
+          options = helper.tax_category_dropdown_options(true)
+          expect(options[:selected]).to be_nil
+        end
+      end
+    end
+
+    context 'when products do not require a tax category' do
+      it 'returns include_blank as the translated "none" string' do
+        options = helper.tax_category_dropdown_options(false)
+        expect(options[:include_blank]).to eq(I18n.t(:none))
+      end
+
+      it 'does not include a selected tax category' do
+        options = helper.tax_category_dropdown_options(false)
+        expect(options[:selected]).to be_nil
+      end
+    end
+  end
+end