fix: Bug creating duplicate category leads to crash screen

app/controllers/categories_controller.rb

@@ -21,6 +21,7 @@ def create
 
       redirect_back_or_to categories_path, notice: t(".success")
     else
+      @categories = Current.family.categories.alphabetically.where(parent_id: nil)
       render :new, status: :unprocessable_entity
     end
   end

test/controllers/categories_controller_test.rb

@@ -33,6 +33,17 @@ class CategoriesControllerTest < ActionDispatch::IntegrationTest
     assert_equal color, new_category.color
   end
 
+  test "create fails if name is not unique" do
+    assert_no_difference "Category.count" do
+      post categories_url, params: {
+        category: {
+          name: categories(:food_and_drink).name,
+          color: Category::COLORS.sample } }
+    end
+
+    assert_response :unprocessable_entity
+  end
+
   test "create and assign to transaction" do
     color = Category::COLORS.sample
 

test/system/categories_test.rb

@@ -0,0 +1,26 @@
+require "application_system_test_case"
+
+class CategoriesTest < ApplicationSystemTestCase
+  setup do
+    sign_in @user = users(:family_admin)
+  end
+
+  test "can create category" do
+    visit categories_url
+    click_link I18n.t("categories.new.new_category")
+    fill_in "Name", with: "My Shiny New Category"
+    click_button "Create Category"
+
+    visit categories_url
+    assert_text "My Shiny New Category"
+  end
+
+  test "trying to create a duplicate category fails" do
+    visit categories_url
+    click_link I18n.t("categories.new.new_category")
+    fill_in "Name", with: categories(:food_and_drink).name
+    click_button "Create Category"
+
+    assert_text "Name has already been taken"
+  end
+end