This is a major rewrite of the billing system. It moves subscription
information off of stripe Subscriptions and into a local CustomerPlan
table.
To keep this manageable, it leaves several things unimplemented
(downgrading, etc), and a variety of other TODOs in the code. There are also
some known regressions, e.g. error-handling on /upgrade is broken.
A lot of the seemingly unrelated test fixture changes are because we're
removing a query to stripe in the upgrade path, in cases when the user's
realm has an existing Customer object.
The fixture changes are because self.upgrade formerly used to cause a page load
of /billing, which in turn calls Customer.retrieve.
If we ran the full test suite with GENERATE_STRIPE_FIXTURES=True, we would
likely see several more Customer.retrieve.N.json's being deleted. But
keeping them there for now to keep the diff small.
f52e9d1 ended up not going far enough. Keeping f52e9d1 in place in case we
ever want to go back to that sort of solution.
Also removes the keep argument from test_billing_quantity_changes_end_to_end,
since that test is actually testing the arguments to
stripe.Subscription.save(), not what is returned by Stripe.
Reran every test with GENERATE_STRIPE_FIXTURES = True, which also caused a
few fixtures to get updates unrelated to these changes (likely due to API
updates that hadn't been previously applied).
When we started the billing system we started by following conventions used
in the Stripe documentation, but in hindsight it makes more sense to follow
conventions used in the Zulip codebase.
This used to be a more likely codepath, before we introduced
Customer.has_billing_relationship. It is no longer literally impossible to
hit this race condition, so I'm not deleting the code, but it's unlikely
enough that it's not worth figuring out how to test it.
Already better tested by the upgrade and downgrade tests using mock_stripe.
Note that the line that was removed is actually not possible to reach, since
canceled subscriptions aren't shown on the Customer object.
Also fixes a bug in process_initial_upgrade. If you have a card on file
(e.g. from a previous subscription), and try to upgrade by billing by
invoice, neither the if nor the elif condition applies.
