add bw-compatibility test

tests/integration/test_backward_compatibility/configs/clusters.xml

@@ -0,0 +1,20 @@
+<clickhouse>
+    <remote_servers>
+        <parallel_replicas>
+            <shard>
+                <replica>
+                    <host>node0</host>
+                    <port>9000</port>
+                </replica>
+                <replica>
+                    <host>node1</host>
+                    <port>9000</port>
+                </replica>
+                <replica>
+                    <host>node2</host>
+                    <port>9000</port>
+                </replica>
+            </shard>
+        </parallel_replicas>
+    </remote_servers>
+</clickhouse>

tests/integration/test_backward_compatibility/test_parallel_replicas_protocol.py

@@ -0,0 +1,64 @@
+import pytest
+
+from helpers.cluster import ClickHouseCluster
+
+
+cluster = ClickHouseCluster(__file__)
+cluster_name = "parallel_replicas"
+nodes = [
+    cluster.add_instance(
+        f"node{num}",
+        main_configs=["configs/clusters.xml"],
+        with_zookeeper=False,
+        image="clickhouse/clickhouse-server",
+        tag="23.11",
+        stay_alive=True,
+        use_old_analyzer=True,
+        with_installed_binary=True,
+    )
+    for num in range(2)
+] + [
+    cluster.add_instance(
+        "node2",
+        main_configs=["configs/clusters.xml"],
+        with_zookeeper=False,
+        use_old_analyzer=True,
+    )
+]
+
+
+@pytest.fixture(scope="module")
+def start_cluster():
+    try:
+        cluster.start()
+        yield cluster
+
+    finally:
+        cluster.shutdown()
+
+
+def test_backward_compatability(start_cluster):
+    for node in nodes:
+        node.query("create table t (a UInt64) engine = MergeTree order by tuple()")
+        node.query("insert into t select number % 100000 from numbers_mt(1000000)")
+
+    # all we want is the query to run without errors
+    for node in nodes:
+        assert (
+            node.query(
+                """
+                select sum(a)
+                from t
+                """,
+                settings={
+                    "cluster_for_parallel_replicas": "parallel_replicas",
+                    "max_parallel_replicas": 3,
+                    "allow_experimental_parallel_reading_from_replicas": 1,
+                    "parallel_replicas_for_non_replicated_merge_tree": 1,
+                },
+            )
+            == "49999500000\n"
+        )
+
+    for node in nodes:
+        node.query("drop table t")