option1.rb

describe "My page" do
  it "lists the item" do
    item = create_item

    within item_row(item) do
      expect(page).to mention_item(item)
    end
  end

  private

  def item_row(item)
    find(".test-item-#{item.id}")
  end

  def mention_item(item)
    have_content(item.title)
  end
end

option2.rb

Capybara.add_selector :item_row do
  css { |item| ".test-item-#{item.id}" }
end

describe "My page" do
  it "lists the item" do
    item = create_item

    within :item_row, item do
      expect(page).to mention_item(item)
    end
  end

  private

  def mention_item(item)
    have_content(item.title)
  end
end