RSPEC - Test to_csv class method

I have this class method in my model:

def self.to_csv
  attributes = %w(title)

  CSV.generate(headers: true) do |csv|
    csv << attributes

    all.each do |campaign|
      csv << campaign.attributes.values_at(*attributes)
    end
  end
end

I'm looking for good ways to test this method with Rspec. Does anyone have good techniques for this method?