billing: Don't check for stripe key and plan objects in tests.

Stripe already returns an appropriate error in prod, and these checks are
just a hassle in tests.

Also fixes an error where the check for Plan.objects.exists() was missing
a "not".

zilencer/lib/stripe.py

@@ -69,14 +69,13 @@ class StripeError(JsonableError):
 def catch_stripe_errors(func: CallableT) -> CallableT:
     @wraps(func)
     def wrapped(*args: Any, **kwargs: Any) -> Any:
-        if not settings.TEST_SUITE and STRIPE_PUBLISHABLE_KEY is None:
-            # Dev-only message; no translation needed.
-            raise StripeError(
-                "Missing Stripe config. See https://zulip.readthedocs.io/en/latest/subsystems/billing.html.")
-
+        if settings.DEVELOPMENT and not settings.TEST_SUITE:  # nocoverage
+            if STRIPE_PUBLISHABLE_KEY is None:
+                raise AssertionError(
+                    "Missing Stripe config. "
+                    "See https://zulip.readthedocs.io/en/latest/subsystems/billing.html.")
             if not Plan.objects.exists():
-            # Dev-only message; no translation needed.
-            raise StripeError(
+                raise AssertionError(
                     "Plan objects not created. Please run ./manage.py setup_stripe")
 
         try:

zilencer/tests/test_stripe.py

@@ -74,24 +74,6 @@ class StripeTest(ZulipTestCase):
             raise_exception()
         mock_billing_logger_error.assert_called()
 
-    @mock.patch("zilencer.lib.stripe.STRIPE_PUBLISHABLE_KEY", None)
-    def test_no_stripe_keys(self) -> None:
-        @catch_stripe_errors
-        def foo() -> None:
-            pass  # nocoverage
-        with self.settings(TEST_SUITE=False):
-            with self.assertRaisesRegex(StripeError, "Missing Stripe config."):
-                foo()
-
-    def test_no_plan_objects(self) -> None:
-        Plan.objects.all().delete()
-
-        @catch_stripe_errors
-        def foo() -> None:
-            pass  # nocoverage
-        with self.assertRaisesRegex(StripeError, "Plan objects not created. Please run ./manage.py"):
-            foo()
-
     @mock.patch("stripe.Customer.create", side_effect=mock_create_customer)
     @mock.patch("stripe.Subscription.create", side_effect=mock_create_subscription)
     def test_initial_upgrade(self, mock_create_subscription: mock.Mock,