Improve Price - AccountActivity model relation

#475

spec/models/account_activity_spec.rb

@@ -0,0 +1,13 @@
+require 'rails_helper'
+
+RSpec.describe AccountActivity do
+  describe 'account validation', db: false do
+    subject(:account_activity) { described_class.new }
+
+    it 'rejects absent' do
+      account_activity.account = nil
+      account_activity.validate
+      expect(account_activity.errors).to have_key(:account)
+    end
+  end
+end