test: Add a test that switching between vnodes and tablets is banned

Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>

test/topology_custom/test_tablets.py

@@ -0,0 +1,25 @@
+#
+# Copyright (C) 2023-present ScyllaDB
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+#
+from cassandra.protocol import InvalidRequest
+from test.pylib.manager_client import ManagerClient
+import pytest
+import logging
+import asyncio
+
+logger = logging.getLogger(__name__)
+
+
+@pytest.mark.asyncio
+async def test_tablet_change_replication_vnode_to_tablets(manager: ManagerClient):
+    cfg = {'enable_user_defined_functions': False,
+           'experimental_features': ['tablets', 'consistent-topology-changes']}
+    server = await manager.server_add(config=cfg)
+
+    cql = manager.get_cql()
+    await cql.run_async("CREATE KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy', 'replication_factor': 1};")
+    with pytest.raises(InvalidRequest):
+        await cql.run_async("ALTER KEYSPACE test WITH replication = {'class': 'NetworkTopologyStrategy', 'replication_factor': 1, 'initial_tablets': 1};")
+