Stripe Customer retrieve stub and expand default_source option

[eliotsykes]

The customer retrieve stub currently doesn't support Stripe's expand: ['default_source'] option:

customer = Stripe::Customer.retrieve(id: 'customer-id-here', expand: ['default_source'])

With fake_stripe and Stripe customer = Stripe::Customer.retrieve(id: 'customer-id-here') (no expand option) the customer.default_source returns a String (the id of the default payment source).

However with Stripe, but not fake_stripe customer = Stripe::Customer.retrieve(id: 'customer-id-here', expand: ['default_source]) (note the expand option) the customer.default_source returns the populated payment source object (not just the string id of the payment source). fake_stripe only returns the String id of the payment source.

(stripe-ruby-mock has a similar issue that may be useful stripe-ruby-mock/stripe-ruby-mock#109 )

[stefannibrasil]

Closing this because fake_stripe has been deprecated: #154