Why Does A Unit Test For destroy_all fail with let? - ruby-on-rails

Question

So I have this model code:
def self.cleanup
Transaction.where("created_at < ?", 30.days.ago).destroy_all
end
and this rspec unit test:
describe 'self.cleanup' do
before(:each) do
#transaction = Transaction.create(seller:item.user, buyer:user, item:item, created_at:6.weeks.ago)
end
it 'destroys all transactions more than 30 days' do
Transaction.cleanup
expect(#transaction).not_to exist_in_database
end
end
with these factories:
FactoryGirl.define do
factory :transaction do
association :seller, factory: :user, username: 'IAMSeller'
association :buyer, factory: :user, username: 'IAmBuyer'
association :item
end
factory :old_transaction, parent: :transaction do
created_at 6.weeks.ago
end
end
using this rspec custom matcher:
RSpec::Matchers.define :exist_in_database do
match do |actual|
actual.class.exists?(actual.id)
end
end
When I change the spec to this:
describe 'self.cleanup' do
let(:old_transaction){FactoryGirl.create(:old_transaction)}
it 'destroys all transactions more than 30 days' do
Transaction.cleanup
expect(old_transaction).not_to exist_in_database
end
end
the test fails. I also tried manually creating a transaction and assigning it to :old_transaction with let() but that makes the test fail too.
Why is it that it only passes when I use an instance variable in the before(:each) block?
Thanks in advance!
EDIT: FAILED OUTPUT
1) Transaction self.cleanup destroys all transactions more than 30 days
Failure/Error: expect(old_transaction).not_to exist_in_database
expected #<Transaction id: 2, seller_id: 3, buyer_id: 4, item_id: 2, transaction_date: nil, created_at: "2014-02-26 10:06:30", updated_at: "2014-04-09 10:06:32", buyer_confirmed: false, seller_confirmed: false, cancelled: false> not to exist in database
# ./spec/models/transaction_spec.rb:40:in `block (3 levels) in <top (required)>'

Answer 1

let is lazy loaded. So in your failing spec this is the order of events:
Transaction.cleanup
old_transaction = FactoryGirl.create(:old_transaction)
expect(old_transaction).not_to exist_in_database
So the transaction is created after you attempt to clean up.
There are multiple options for you:
Don't use let for this
Unless you have other specs that you want to tell other devs:
I fully intend for all of these specs to reference what should be the exact same object
I personally feel, that you're better off inlining the transaction.
it do
transaction = FactoryGirl.create(:old_transaction)
Transaction.cleanup
expect(transaction).not_to exist_in_database
end
Use the change matcher
This is my personal choice as it clearly demonstrates the intended behavior:
it do
expect{
Transaction.cleanup
}.to change{ Transaction.exists?(old_transaction.id) }.to false
end
This works with let as the change block is run before AND after the expect block. So on the first pass the old_transaction is instantiated so it's id can be checked.
Use before or reference old_transaction before your cleanup
IMO this seems odd:
before do
old_transaction
end
it do
old_transaction # if you don't use the before
Transaction.clean
# ...
end
Use let!
The let! is not lazy loaded. Essentially, it's an alias for doing a normal let, then calling it in a before. I'm not a fan of this method (see The bang is for surprise for details why).

Answer 2

I think you've just accidentally typoed in a ":"
Try this spec:
describe 'self.cleanup' do
let(:old_transaction){FactoryGirl.create(:old_transaction)}
it 'destroys all transactions more than 30 days' do
Transaction.cleanup
expect(old_transaction).not_to exist_in_database
end
end