billing: Create is_sponsored_realm function.

corporate/lib/stripe.py

@@ -876,6 +876,10 @@ def approve_sponsorship(realm: Realm, *, acting_user: Optional[UserProfile]) ->
             internal_send_private_message(notification_bot, billing_admin, message)
 
 
+def is_sponsored_realm(realm: Realm) -> bool:
+    return realm.plan_type == Realm.STANDARD_FREE
+
+
 def get_discount_for_realm(realm: Realm) -> Optional[Decimal]:
     customer = get_customer_by_realm(realm)
     if customer is not None:

corporate/tests/test_stripe.py

@@ -38,6 +38,7 @@ from corporate.lib.stripe import (
     invoice_plan,
     invoice_plans_as_needed,
     is_realm_on_free_trial,
+    is_sponsored_realm,
     make_end_of_cycle_updates_if_needed,
     next_month,
     process_initial_upgrade,
@@ -3005,6 +3006,14 @@ class BillingHelpersTest(ZulipTestCase):
         plan.save(update_fields=["status"])
         self.assertTrue(is_realm_on_free_trial(realm))
 
+    def test_is_sponsored_realm(self) -> None:
+        realm = get_realm("zulip")
+        self.assertFalse(is_sponsored_realm(realm))
+
+        realm.plan_type = Realm.STANDARD_FREE
+        realm.save()
+        self.assertTrue(is_sponsored_realm(realm))
+
 
 class LicenseLedgerTest(StripeTestCase):
     def test_add_plan_renewal_if_needed(self) -> None:

corporate/views.py

@@ -22,6 +22,7 @@ from corporate.lib.stripe import (
     downgrade_at_the_end_of_billing_cycle,
     downgrade_now_without_creating_additional_invoices,
     get_latest_seat_count,
+    is_sponsored_realm,
     make_end_of_cycle_updates_if_needed,
     process_initial_upgrade,
     renewal_amount,
@@ -190,7 +191,7 @@ def initial_upgrade(request: HttpRequest) -> HttpResponse:
             billing_page_url = f"{billing_page_url}?onboarding=true"
         return HttpResponseRedirect(billing_page_url)
 
-    if user.realm.plan_type == user.realm.STANDARD_FREE:
+    if is_sponsored_realm(user.realm):
         return HttpResponseRedirect(billing_page_url)
 
     percent_off = Decimal(0)