billing: Wrap make_end_of_cycle_updates_if_needed with transaction.atomic.

Otherwise, the plan would be left in an inconsistent state if one of the
queries fail.

corporate/lib/stripe.py

@@ -243,6 +243,7 @@ def do_replace_payment_source(user: UserProfile, stripe_token: str,
 
 # event_time should roughly be timezone_now(). Not designed to handle
 # event_times in the past or future
+@transaction.atomic
 def make_end_of_cycle_updates_if_needed(plan: CustomerPlan,
                                         event_time: datetime) -> Tuple[Optional[CustomerPlan], Optional[LicenseLedger]]:
     last_ledger_entry = LicenseLedger.objects.filter(plan=plan).order_by('-id').first()

corporate/tests/test_stripe.py

@@ -1374,6 +1374,10 @@ class StripeTest(StripeTestCase):
         self.assertEqual(annual_ledger_entries.values_list('licenses', 'licenses_at_next_renewal')[0], (20, 20))
         self.assertEqual(annual_ledger_entries[1].is_renewal, False)
         self.assertEqual(annual_ledger_entries.values_list('licenses', 'licenses_at_next_renewal')[1], (25, 25))
+        audit_log = RealmAuditLog.objects.get(event_type=RealmAuditLog.CUSTOMER_SWITCHED_FROM_MONTHLY_TO_ANNUAL_PLAN)
+        self.assertEqual(audit_log.realm, user.realm)
+        self.assertEqual(ujson.loads(audit_log.extra_data)["monthly_plan_id"], monthly_plan.id)
+        self.assertEqual(ujson.loads(audit_log.extra_data)["annual_plan_id"], annual_plan.id)
 
         invoice_plans_as_needed(self.next_month)
 
@@ -1491,7 +1495,6 @@ class StripeTest(StripeTestCase):
             response = self.client_get("/billing/")
         self.assert_in_success_response(["be switched from monthly to annual billing on <strong>February 2, 2012"], response)
 
-        with patch('corporate.lib.stripe.timezone_now', return_value=self.next_month):
         invoice_plans_as_needed(self.next_month)
 
         self.assertEqual(LicenseLedger.objects.filter(plan=monthly_plan).count(), 1)
@@ -1514,7 +1517,8 @@ class StripeTest(StripeTestCase):
         self.assertEqual(annual_ledger_entries.values_list('licenses', 'licenses_at_next_renewal')[0], (num_licenses, num_licenses))
         self.assertEqual(annual_plan.invoiced_through, None)
 
-        with patch('corporate.lib.stripe.timezone_now', return_value=self.next_month):
+        # First call of invoice_plans_as_needed creates the new plan. Second call
+        # calls invoice_plan on the newly created plan.
         invoice_plans_as_needed(self.next_month + timedelta(days=1))
 
         annual_plan.refresh_from_db()

corporate/views.py

@@ -204,6 +204,7 @@ def billing_home(request: HttpRequest) -> HttpResponse:
         if last_ledger_entry is not None:
             if new_plan is not None:  # nocoverage
                 plan = new_plan
+            assert(plan is not None)  # for mypy
             plan_name = {
                 CustomerPlan.STANDARD: 'Zulip Standard',
                 CustomerPlan.PLUS: 'Zulip Plus',