Stubbing with arguments - examples used in my "(More) Specific Stubbing with RSpec" blog post

stubbing_with_arguments_spec.rb

class GivesCreditToPreferredCustomers
  LOOK_BACK_PERIOD = 3
  def self.for_large_orders(sales_amount, added_credit)
    # the has_large_purchases scope now takes two arguments
    preferred_customers = Customer.has_large_purchases(sales_amount, LOOK_BACK_PERIOD)
    preferred_customers.each do |customer|
      customer.add_credit added_credit
    end
  end
end

class Customer
  attr_reader :total_credit

  def self.has_large_purchases(sales_amount)
    puts "AR query to find buyers with large purchases"
  end

  def add_credit(amount)
    @total_credit = 0 if @total_credit.nil?
    @total_credit += amount
  end
end

describe GivesCreditToPreferredCustomers do
  context "for large orders" do
    let(:sales_amount) { 10000 }
    let(:credit_given) { 100 }
    let(:found_customer) { Customer.new }

    before do
      Customer.stub(:has_large_purchases).and_return [found_customer]
    end 

    it "update's the customer's credit" do
      GivesCreditToPreferredCustomers \
            .for_large_orders(sales_amount, credit_given)

      found_customer.total_credit.should == credit_given
    end

    it "scans over the past three units" do
      look_back_period = 3
  
      # rspec will use the return value from an existing stub, if any
      Customer.should_receive(:has_large_purchases).with(sales_amount, look_back_period)
      
      GivesCreditToPreferredCustomers.for_large_orders(sales_amount, credit_given)
    do
  end
end