Agile Web Development with Rails 4 - Iteration E3 Unit Tests - ruby-on-rails

Question

I'm new to Ruby on Rails and reading the book "Agile Web Development with Rails 4". As doing the "Playtime" exercises at the end of chapter 10 (Iteration E3 - Finishing the Cart), I stumbled across some problems.
One of it is in the 2nd exercise, where one should create unit tests to add unique and duplicate products to some shopping cart.
When one adds a product to that cart, it might be the first product of that kind and so the amount is one, but every additional add-operation increases the quantity. This works fine in browser-testing, but my test-cases fail.
Testcase:
test 'duplicates must not be saved as a new line item' do
# create cart and add one product
cart = new_cart_with_one_product(:ruby)
assert cart.save
assert_equal 1, cart.line_items.count
assert_equal 1, cart.line_items.find_by(
product_id: products(:ruby).id).quantity
assert_equal 49.50, cart.total_price.to_f
# ----------------------------------------------------------------
# create a second (actually the same product) and add it to cart:
item = products(:ruby)
cart.add_product(item.id, item.price)
assert cart.save
assert_equal 1, cart.line_items.count, 'duplicate saved as new line'
# test FAILS at the next two lines:
assert_equal 2, cart.line_items.find_by(product_id: item.id).quantity,
'quantity has not been increased'
assert_equal 99.00, cart.total_price.to_f, 'total price is wrong'
end
It tells me that the expected value is 2, but the actual value is 1.
So the quantity has not been increased. The total price does not change either, though both things work in the development-environment.
Here is the code of the Cart-Model:
class Cart < ActiveRecord::Base
has_many:line_items, dependent: :destroy
def add_product(product_id, product_price)
current_item = line_items.find_by(product_id: product_id)
if current_item
current_item.quantity +=1
else
# create a new line_item
current_item = line_items.build(product_id: product_id,
price: product_price)
end
current_item
end
def total_price
line_items.to_a.sum {|item| item.total_price }
end
end
I am using Rails 4.2.5 on Ruby 2.2.3.
I hope somebody can help me with that, because I do not understand why this is happening in the test-environment and using rake test only. If you need any additional code, please let me know.

Answer 1

I finally found my mistake:
The quantity is incremented in the model, for sure, but it isn't saved there.
It is saved in the controller, so this step is totally bypassed in my test because it just tests the model itself.
To fix the test, I changed cart.add_product(item.id, item.price)to cart.add_product(item.id, item.price).save to fix that issue.
I also reloaded the cart before testing, because otherwise it calculates the old total price (thanks to #PrakashMurthy though it should solve another issue, but at the end it helped :-) ).
The (working) Testcase looks like this, now:
test 'duplicates must not be saved as a new line item' do
# create cart and add one product
cart = new_cart_with_one_product(:ruby)
assert cart.save
assert_equal 1, cart.line_items.count
assert_equal 1, cart.line_items.find_by(
product_id: products(:ruby).id).quantity
assert_equal 49.50, cart.total_price.to_f
# ----------------------------------------------------------------
# create a second (actually the same product) and add it to cart:
item = products(:ruby)
# the following two lines do the trick:
cart.add_product(item.id, item.price).save
cart.reload
assert cart.save
assert_equal 1, cart.line_items.count, 'duplicate saved as new line'
assert_equal 2, cart.line_items.find_by(product_id: item.id).quantity,
'quantity has not been increased'
assert_equal 99.00, cart.total_price.to_f, 'total price is wrong'
end