FIX: Fix for Default to subcategory when parent category does not allow posting (#21537)

* FIX: Fix for Default to subcategory when parent category does not allow posting

* added tests for edge case scenario

* implemented correct behaviour when parent category doesn't have subcategories

* implemented new fabricator for categories and suggested changes

spec/system/composer/default_to_subcategory_spec.rb

@@ -6,32 +6,63 @@ describe "Default to Subcategory when parent Category doesn't allow posting",
   fab!(:user) { Fabricate(:user) }
   fab!(:group) { Fabricate(:group) }
   fab!(:group_user) { Fabricate(:group_user, user: user, group: group) }
+  fab!(:default_latest_category) { Fabricate(:category) }
   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
+  fab!(:category_with_no_subcategory) do
+    Fabricate(:category_with_group_and_permission, group: group, permission_type: 3)
+  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)
+  describe "anon user" do
+    it "can visit the category" do
+      category_page.visit(category_with_no_subcategory)
+      select_kit = PageObjects::Components::SelectKit.new(page.find(".navigation-container"))
+      expect(select_kit).to have_selected_value(category_with_no_subcategory.id)
     end
   end
 
-  describe "Setting disabled and can't post on parent category" do
-    before { SiteSetting.default_subcategory_on_read_only_category = false }
+  describe "logged in user" do
+    before { sign_in(user) }
+    describe "default_subcategory_on_read_only_category setting enabled and can't post on parent category" do
+      before do
+        SiteSetting.default_subcategory_on_read_only_category = true
+        SiteSetting.default_composer_category = default_latest_category.id
+      end
+      describe "Category has subcategory" do
+        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 "Category does not have subcategory" do
+        it "should have the 'New Topic' button enabled and default Subcategory set to latest default subcategory" do
+          category_page.visit(category_with_no_subcategory)
+          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(default_latest_category.id)
+        end
+      end
+    end
 
-    it "should have 'New Topic' button disabled" do
-      category_page.visit(category)
-      expect(category_page).to have_button("New Topic", disabled: true)
+    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
 end