I was getting Stripe::InvalidRequestError: You must supply either a card or a customer id error. To fix this, make sure js is true in your integration test like this:
feature 'Guest Checkout' do
scenario 'Complete purchase of one product', js: true do
visit products_show_path
click_link 'Buy Now'
fill_in "Card Number", with: '4242424242424242'
page.select '10', from: "card_month"
page.select '2029', from: 'card_year'
click_button 'Buy Now'
expect(page).to have_content('Receipt')
end
end
