billing: Create is_realm_on_free_trial helper function.

corporate/lib/stripe.py

@@ -785,6 +785,11 @@ def invoice_plans_as_needed(event_time: datetime = timezone_now()) -> None:
         invoice_plan(plan, event_time)
 
 
+def is_realm_on_free_trial(realm: Realm) -> bool:
+    plan = get_current_plan_by_realm(realm)
+    return plan is not None and plan.is_free_trial()
+
+
 def attach_discount_to_realm(
     realm: Realm, discount: Decimal, *, acting_user: Optional[UserProfile]
 ) -> None:

corporate/tests/test_stripe.py

@@ -35,6 +35,7 @@ from corporate.lib.stripe import (
     get_realms_to_default_discount_dict,
     invoice_plan,
     invoice_plans_as_needed,
+    is_realm_on_free_trial,
     make_end_of_cycle_updates_if_needed,
     next_month,
     process_initial_upgrade,
@@ -2969,6 +2970,24 @@ class BillingHelpersTest(ZulipTestCase):
             },
         )
 
+    def test_is_realm_on_free_trial(self) -> None:
+        realm = get_realm("zulip")
+        self.assertFalse(is_realm_on_free_trial(realm))
+
+        customer = Customer.objects.create(realm=realm, stripe_customer_id="cus_12345")
+        plan = CustomerPlan.objects.create(
+            customer=customer,
+            status=CustomerPlan.ACTIVE,
+            billing_cycle_anchor=timezone_now(),
+            billing_schedule=CustomerPlan.ANNUAL,
+            tier=CustomerPlan.STANDARD,
+        )
+        self.assertFalse(is_realm_on_free_trial(realm))
+
+        plan.status = CustomerPlan.FREE_TRIAL
+        plan.save(update_fields=["status"])
+        self.assertTrue(is_realm_on_free_trial(realm))
+
 
 class LicenseLedgerTest(StripeTestCase):
     def test_add_plan_renewal_if_needed(self) -> None: