Michal Oláh crafting applications

Stubbing external services

28 Nov 2013

This post takes a little detour into (IMHO) the best way of stubbing an external resource like a payment gateway.

Testing with VCR

Recently I was implementing a subscription service into a product and I decided to use Braintree. They provide a nice ruby wrapper library and a sandbox to test your functionality before you go live. Testing the implementation is a whole another story. One witch I’m gonna go into in this post.

Testing external services should be done by not directly stubbing the calls to the library. Instead it should be accomplished by either stubbing the http (or any other network protocol) calls or recording the intercactions and playing them back. Avdi Grimm has a good freebee episode of Ruby Tapas on the matter.

I went ahead and started using the most popular record-playback stubbing library around VCR. This meant we could write our tests and after they ran successfully for the first time, they would run like that forever. There are a couple of edge cases that cannot be reasonably dealt with just by using the record-playback technique.

Trouble testing

The most common case I have come across where the record-playback technique does not work is when you need to get an external system into a state which is not easily achievable. E.g. you want to retry a subscription payment when the payment is past due. More on Braintree payments can be found here.

authorized_transaction = Braintree::Subscription.retry_charge(
  subscription.id
).transaction
result = Braintree::Transaction.submit_for_settlement(
  authorized_transaction.id
)
result.success?
#=> true

The sandbox does not include an option to change this property of a payment (or to simulate a recurring transaction) which means the only way is to setup a subscription that will fail for the next the day, let it fail and run the test that retries the transaction on the next day. This is both cumbersome and error-prone.

fake_braintree

During development I read a blog post on the Toughtbot blog which got me thingking and eventually rolling my own little braintree sandbox stub. This got me thinking again - someone else must have encountered this problem and solve it somehow (perhaps much better than me). This lead me to to discover the Fake Braintree gem. The gem encapsulated everything I did with my little solution and some more. Despite being exactly what I needed, there were some problems getting it to do what I needed. I would like to note those here for my (and perhaps others) future reference.

fake_braintree documentation

Since the documentation is mostly in the form of a github readme I was left on my own go through the codebase. Not a problem, here is what I found.

Creating a braintree customer

The first order of business is creating a customer for us to be interacting with. The easiest way I found was to create is manually within fake_braintree:

customer = FakeBraintree::Customer.new({'credit_card' =>
                                         {
                                           'number' => '4111111111111111',
                                           'expiration_month' => '12',
                                           'expiration_year' => '2015'
                                         }
                                       },
                                       {id: '42'})
customer.create

#=> {"Content-Encoding"=>"gzip"}, "..."]

This creates a customer along with a default credit card and an id we controll. Note that the return value is the same as if we hit the real braintree endpoint. This means that the following call will return the customer we just created.

customer = Braintree::Customer.find('42')
#=> #<Braintree::Customer id: "42", company: nil, email: nil, fax: nil, first_name: nil, last_name: nil, phone: nil, website: nil, created_at: nil, updated_at: nil, addresses: [], credit_cards: [#<Braintree::CreditCard token: "5910f4ea0062a0e29afd3dccc741e3ce", billing_address: nil, bin: "411111", card_type: nil, cardholder_name: nil, created_at: nil, customer_id: "42", expiration_month: "12", expiration_year: "2015", last_4: "1111", updated_at: nil, prepaid: nil, payroll: nil, commercial: nil, debit: nil, durbin_regulated: nil, healthcare: nil, country_of_issuance: nil, issuing_bank: nil, image_url: nil>]>

customer.default_credit_card
#=> #<Braintree::CreditCard token: "5910f4ea0062a0e29afd3dccc741e3ce", billing_address: nil, bin: "411111", card_type: nil, cardholder_name: nil, created_at: nil, customer_id: "42", expiration_month: "12", expiration_year: "2015", last_4: "1111", updated_at: nil, prepaid: nil, payroll: nil, commercial: nil, debit: nil, durbin_regulated: nil, healthcare: nil, country_of_issuance: nil, issuing_bank: nil, image_url: nil>

Creating a subscription

Creating subscriptions is a little more tricky. You need a payment method token (which can be obtained from a customer’s credit card) and a plan id. Continuing from the last example

subscription = Braintree::Subscription.create(payment_method_token: customer.default_credit_card.token,
                               plan_id: 'my_plan_id').subscription

Now you can run the Braintree retry_charge method on the subscription as if the subscription was past due. If you tried to retry_charge on a subscription in the Braintree sandbox, you would get an error.

authorized_transaction = Braintree::Subscription.retry_charge(
  subscription_id,
  price
).transaction

# Run the code with fake_braintree
#=> #<Braintree::Transaction id: "2a55837dd3f2a63a64c23107afecdd95", type: "sale", amount: "10.0", status: "authorized", created_at: nil, credit_card_details: #<token: nil, bin: nil, last_4: nil, card_type: nil, expiration_date: "/", cardholder_name: nil, customer_location: nil, prepaid: nil, healthcare: nil, durbin_regulated: nil, debit: nil, commercial: nil, payroll: nil, country_of_issuance: nil, issuing_bank: nil>, customer_details: #<id: nil, first_name: nil, last_name: nil, email: nil, company: nil, website: nil, phone: nil, fax: nil>, subscription_details: #<Braintree::Transaction::SubscriptionDetails:0x007fd892886ae0>, updated_at: nil>

# Run the code with the real endpoint
#=> #<Braintree::ErrorResult params:{...} errors:<transaction:[(91531) Subscription status must be Past Due in order to retry.]>>


authorized_transaction = Braintree::Subscription.retry_charge(subscription_id, 42.0).transaction
result = Braintree::Transaction.submit_for_settlement(
  authorized_transaction.id
)
#=> true

To be fair, you cannot retry_charge with the current released version of the fake_braintree gem. I needed this to work, so I created a fork where I implemented the functionality https://github.com/m1k3/fake_braintree. I may get around to submitting a pull-request, but in the meantime use my forked repo instead of the official gem.

fake_braintree gotchas

So far I only found one gotcha. I may get around to fixing it (and submitting a pull-request), but in the mean time one has to work around the problem. In the examples above we created a subscription. In a real Braintree endpoint this subscription would get added to the credit cards subscriptions. This means that after creating the subscription and searching for customer information again we should not get an empty array of subscriptions see BT documentation.

customer = Braintree::Customer.find('42')
customer.default_credit_card.subscriptions
#=> []
# this should be
#[<Braintree::CreditCard token: "5910f4ea0062a0e29afd3dccc741e3ce", billing_address: nil, bin: "411111", card_type: nil, cardholder_name: nil, created_at: nil, customer_id: "42", expiration_month: "12", expiration_year: "2015", last_4: "1111", updated_at: nil, prepaid: nil, payroll: nil, commercial: nil, debit: nil, durbin_regulated: nil, healthcare: nil, country_of_issuance: nil, issuing_bank: nil, image_url: nil>]

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