rspec mocking issue

refund.rb

def refund
  self.items

  ActiveRecord::Base.transaction do
    self.items.each { |i| i.update!(refund: true) }
  end
end

def refund_v2
  refundable_items = self.items.where(refund: false)

  ActiveRecord::Base.transaction do
    refundable_items.each { |i| i.update!(refund: true) }
  end
end

refund_spec.rb

self.items.first.stub(:create_or_update).and_return false

expect(refund).to eq false # passes
expect(refund_v2).to eq false # fails