payment_steps.rb

Transform /^\$[.\d]+$/ do |dollars|
  dollars.to_money
end

Transform /^card "([\d\s]*)"$/ do |cc_number|
  ActiveMerchant::Billing::CreditCard.new :number => cc_number.gsub(/\D/, '')
end

Then /^the (card "[\d\s]*") should be charged (\$[.\d]+)$/ do |credit_card, price|
  credit_card.class # => ActiveMerchant::Billing::CreditCard
  price.class # => Money
end

test.feature

  Scenario: Register
    ...
    Then the card "4111 1111 1111 1111" should be charged $20.00