[python] Add mock API tests for service/multiple-services Spector scenario (#10258)

Adds Python SDK mock API tests for the
[`service/multiple-services`](Azure/typespec-azure#4158)
Spector scenario, which tests that multiple services defined without an
explicit `@client` decorator generate separate root clients.

## Changes

- **`regenerate-common.ts`**: Added `service/multiple-services` entry
with namespace `service.multipleservices`
- **New tests** (`test_service_multiple_services.py` + async
counterpart): Validates that both `ServiceAClient` and `ServiceBClient`
are generated as separate root clients, and verifies
`ServiceBClient.operations.op_b()` and
`ServiceBClient.sub_namespace.sub_op_b()` — correct `api-version=bv2`
succeeds (204), wrong `api-version=bv1` raises `HttpResponseError`
- **Changelog entry**: Added internal changelog for
`@typespec/http-client-python`

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: msyyc <70930885+msyyc@users.noreply.github.com>
Co-authored-by: Yuchao Yan <yuchaoyan@microsoft.com>

Author: Copilot

.chronus/changes/python-add-test-service-multiple-services-2026-4-2-22-40-0.md

@@ -0,0 +1,7 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/http-client-python"
+---
+
+Add mock API tests for `service/multiple-services` scenario (multiple services without explicit `@client`).

packages/http-client-python/eng/scripts/ci/regenerate-common.ts

@@ -135,6 +135,9 @@ export const BASE_AZURE_EMITTER_OPTIONS: Record<
   "service/multi-service": {
     namespace: "service.multiservice",
   },
+  "service/multiple-services": {
+    namespace: "service.multipleservices",
+  },
 };
 
 export const BASE_EMITTER_OPTIONS: Record<

packages/http-client-python/tests/mock_api/azure/asynctests/test_service_multiple_services_async.py

@@ -0,0 +1,44 @@
+# -------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for
+# license information.
+# --------------------------------------------------------------------------
+import pytest
+from azure.core.exceptions import HttpResponseError
+from service.multipleservices.aio import ServiceAClient, ServiceBClient
+from service.multipleservices.models import VersionsB
+
+
+@pytest.fixture
+def service_b_client():
+    """Fixture that creates a ServiceBClient for testing."""
+    return ServiceBClient(endpoint="http://localhost:3000")
+
+
+@pytest.mark.asyncio
+async def test_service_multiple_services_both_clients_exist():
+    """Verify that multiple services without explicit @client create separate root clients."""
+    async with ServiceAClient(endpoint="http://localhost:3000") as a_client:
+        assert a_client is not None
+    async with ServiceBClient(endpoint="http://localhost:3000") as b_client:
+        assert b_client is not None
+
+
+@pytest.mark.asyncio
+async def test_service_multiple_services_operation_b(service_b_client):
+    async with service_b_client:
+        async with ServiceBClient(endpoint="http://localhost:3000", api_version=VersionsB.BV1) as wrong_client:
+            with pytest.raises(HttpResponseError):
+                await wrong_client.operations.op_b()
+
+        await service_b_client.operations.op_b()
+
+
+@pytest.mark.asyncio
+async def test_service_multiple_services_sub_namespace_operation_b(service_b_client):
+    async with service_b_client:
+        async with ServiceBClient(endpoint="http://localhost:3000", api_version=VersionsB.BV1) as wrong_client:
+            with pytest.raises(HttpResponseError):
+                await wrong_client.sub_namespace.sub_op_b()
+
+        await service_b_client.sub_namespace.sub_op_b()

packages/http-client-python/tests/mock_api/azure/test_service_multiple_services.py

@@ -0,0 +1,40 @@
+# -------------------------------------------------------------------------
+# Copyright (c) Microsoft Corporation. All rights reserved.
+# Licensed under the MIT License. See License.txt in the project root for
+# license information.
+# --------------------------------------------------------------------------
+import pytest
+from azure.core.exceptions import HttpResponseError
+from service.multipleservices import ServiceAClient, ServiceBClient
+from service.multipleservices.models import VersionsB
+
+
+@pytest.fixture
+def service_b_client():
+    """Fixture that creates a ServiceBClient for testing."""
+    with ServiceBClient(endpoint="http://localhost:3000") as client:
+        yield client
+
+
+def test_service_multiple_services_both_clients_exist():
+    """Verify that multiple services without explicit @client create separate root clients."""
+    with ServiceAClient(endpoint="http://localhost:3000") as a_client:
+        assert a_client is not None
+    with ServiceBClient(endpoint="http://localhost:3000") as b_client:
+        assert b_client is not None
+
+
+def test_service_multiple_services_operation_b(service_b_client):
+    with ServiceBClient(endpoint="http://localhost:3000", api_version=VersionsB.BV1) as wrong_client:
+        with pytest.raises(HttpResponseError):
+            wrong_client.operations.op_b()
+
+    service_b_client.operations.op_b()
+
+
+def test_service_multiple_services_sub_namespace_operation_b(service_b_client):
+    with ServiceBClient(endpoint="http://localhost:3000", api_version=VersionsB.BV1) as wrong_client:
+        with pytest.raises(HttpResponseError):
+            wrong_client.sub_namespace.sub_op_b()
+
+    service_b_client.sub_namespace.sub_op_b()