FEATURE: Default to subcategory when parent category does not allow posting (#21228)

added site toggle functionality through site settings

added tests to implemented feature

Introduced suggested correction

renamed find_new_topic method and deleted click_new_topic_button method

spec/system/composer/default_to_subcategory_spec.rb

@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+describe "Default to Subcategory when parent Category doesn't allow posting",
+         type: :system,
+         js: true do
+  fab!(:user) { Fabricate(:user) }
+  fab!(:group) { Fabricate(:group) }
+  fab!(:group_user) { Fabricate(:group_user, user: user, group: group) }
+  fab!(:category) { Fabricate(:private_category, group: group, permission_type: 3) }
+  fab!(:subcategory) do
+    Fabricate(:private_category, parent_category_id: category.id, group: group, permission_type: 1)
+  end
+  let(:category_page) { PageObjects::Pages::Category.new }
+  before { sign_in(user) }
+
+  describe "Setting enabled and can't post on parent category" do
+    before { SiteSetting.default_subcategory_on_read_only_category = true }
+
+    it "should have 'New Topic' button enabled and default Subcategory set in the composer" do
+      category_page.visit(category)
+      expect(category_page).to have_button("New Topic", disabled: false)
+      category_page.new_topic_button.click
+      select_kit =
+        PageObjects::Components::SelectKit.new(page.find("#reply-control.open .category-chooser"))
+      expect(select_kit).to have_selected_value(subcategory.id)
+    end
+  end
+
+  describe "Setting disabled and can't post on parent category" do
+    before { SiteSetting.default_subcategory_on_read_only_category = false }
+
+    it "should have 'New Topic' button disabled" do
+      category_page.visit(category)
+      expect(category_page).to have_button("New Topic", disabled: true)
+    end
+  end
+end