Fix UnitsiTest#test_index

app/models/unit.rb

@@ -3,7 +3,7 @@ class Unit < ApplicationRecord
 
   belongs_to :user, optional: true
   belongs_to :base, optional: true, class_name: "Unit"
-  has_many :subunits, class_name: "Unit", dependent: :restrict_with_error, inverse_of: :base
+  has_many :subunits, class_name: "Unit", inverse_of: :base, dependent: :restrict_with_error
 
   validate if: ->{ base.present? } do
     errors.add(:base, :user_mismatch) unless user == base.user

test/system/units_test.rb

@@ -12,7 +12,8 @@ class UnitsTest < ApplicationSystemTestCase
       assert_selector 'tr', count: @user.units.count
     end
 
-    Unit.destroy_all
+    # Cannot #destroy_all due to {dependent: :restrict*} on Unit.subunits association
+    @user.units.delete_all
     visit units_path
     within 'tbody' do
       assert_selector 'tr', count: 1