Controller に書いた helper メソッドを view spec で stub する

# ApplicationController

def user_logged_in?
 'hoge'
end

helper_method :user_logged_in?

# header.html.slim_spec.rb

RSpec.describe 'application/_header', type: :view do
  let(:user) { create(:user) }

  subject do
    render partial: 'application/header'
  end
  before { stub_helper_method }

  def stub_helper_method
    controller.singleton_class.class_exec do
      helper_method :user_logged_in?
      define_method :user_logged_in? do
        'stub'
      end
    end
  end

  context 'not signed in' do
    before do
      allow(view).to receive(:user_logged_in?).and_return(false)
    end

    it do
      is_expected.to have_link 'ログイン', href: new_user_session_path
    end
  end

純粋に以下のみで試みると
allow(view).to receive(:user_logged_in?).and_return(false)

=> does not implement: user_logged_in?

と返されるため。