What happen if we do operations on mocked objects? Rspec - ruby

Question

Firsty I would say that I'm learning Ruby and TDD program, so please be forgiving for me. Acctualy I have two questions releted with each other but firsty please take a look on this code. Its part of my unit test for class Order:
context 'with products' do
let(:result) { instance_double('Money', value: 20, currency: 'EUR') }
let(:xxx) { instance_double('Money', value: 10, currency: 'EUR') }
let(:money2) { instance_double('Money', value: 10, currency: 'EUR',:+ => xxx , :to_s => '10.00 EUR' ) }
let(:money) { instance_double('Money', value: 10, currency: 'EUR', :+ => money2, :to_s => '10.00 EUR') }
let(:product1) { instance_double('Product', price: money2) }
let(:product2) { instance_double('Product', price: money) }
let(:products) { [product1, product2] }
it 'returns sum of product prices' do
#Real objects
product1 = Product.new
product1.price = Money.new('1.23', 'EUR')
product1.name = product1
product2 = Product.new
product2.price = Money.new('1.23', 'EUR')
product2.name = product2
products1 = [product1,product2]
puts products1.map!(&:price)
#Fake
puts "fakeproducts map"
fakeproducts = products.map!(&:price)
puts fakeproducts
puts "Sum of fakeproducts"
puts Money.sum(fakeproducts)
puts Money.sum(fakeproducts).to_s
puts "methods of sum fakeproducts"
puts Money.sum(fakeproducts).methods
expect(Order.new(full_name, date, products).total_amount).to eql result
end
end
Problem is that my real objects works,but mocked objects doens't . Error which I got:
Failure/Error: expect(Order.new(full_name, date, products).total_amount).to eql result
Double "Money (instance)" received unexpected message :price with (no args)
Total_amount function:
def total_amount
return 0 if products.empty?
asd = products.map!(&:price)
Money.sum(asd)
end
and Money.sum looks like this:
def self.sum(moneys)
moneys.group_by(&:currency).values.map(&:sum)
end
I suspect that, when I do some operations on my mocked object it lose its properties.
The questions are:
Is it normal that this things happen?
What is Solutions for this problem? Should I mock result of my function?

Answer 1

Your use of map! in total_amount is clobbering the products associated with the order, replacing them with their price, so that the next time you call price on the order's products (e.g. as in a subsequent call to total_amount), you are sending price to one of your money doubles.
You can avoid this particular symptom by using map instead of map! inside of total_amount.
As a related side, it's much easier to provide help with these kinds of questions if you provide the stack trace with your error and identify the corresponding source lines in your code.