best way to test a factory method

factoryspec.rb

class Pipeline
  def self.run
    new.run
  end
  
  def run
    # do stuff
  end
end

RSpec.describe Pipeline do
  subject { described_class }
  
  # rubocop fails this
  it 'runs a new instance' do
    expect(subject).to receive_message_chain(:new, :run)
    subject.run
  end

   # and fails this
  it 'runs a new instance' do
    expect_any_instance_of(subject).to receive(:run)
    subject.run
  end
end