fix: import and use asyncio for async service test

Author: vchudnov-g

gapic/templates/noxfile.py.j2

@@ -55,6 +55,7 @@ SYSTEM_TEST_PYTHON_VERSIONS: List[str] = ["3.8", "3.9", "3.10", "3.11", "3.12",
 SYSTEM_TEST_STANDARD_DEPENDENCIES = [
     "mock",
     "pytest",
+    "pytest-asyncio"
     "google-cloud-testutils",
 ]
 SYSTEM_TEST_EXTERNAL_DEPENDENCIES: List[str] = []

gapic/templates/tests/unit/gapic/%name_%version/%sub/test_%service.py.j2

@@ -226,6 +226,7 @@ def test__get_api_endpoint():
 {% for method in service.methods.values() %}{% with method_name = method.name|snake_case %}
 {% for mode in ["", "async"] %}
 {% if mode == "async" %}
+@pytest.mark.asyncio
 async def test_{{ method_name }}_api_version_header_async(transport_name="grpc"):
     client = {{ service.async_client_name }}(credentials=async_anonymous_credentials(), transport=transport_name)
 {% else %}
@@ -247,7 +248,8 @@ def test_{{ method_name }}_api_version_header(transport_name):
         # Mock the actual call within the gRPC stub, and fake the request.
         with mock.patch.object(
                 type(client.transport.{{ method.transport_safe_name|snake_case }}),
-                '__call__'
+                '__call__'{% if mode == "async" %},
+                new_callable=AsyncMock{% endif %}
             ) as call:
             {% if mode == "async" %}
                 await client.{{ method_name }}()

noxfile.py

@@ -167,7 +167,7 @@ def fragment(session, use_ads_templates=False):
         "pytest-cov",
         "pytest-xdist",
         "asyncmock; python_version < '3.8'",
-        "pytest-asyncio < '1.1.0'",
+        "pytest-asyncio<1.1.0",
         "grpcio-tools",
     )
     session.install("-e", ".")
@@ -480,7 +480,7 @@ def run_showcase_unit_tests(session, fail_under=100, rest_async_io_enabled=False
         "pytest-cov",
         "pytest-xdist",
         "asyncmock; python_version < '3.8'",
-        "pytest-asyncio < '1.1.0'",
+        "pytest-asyncio<1.1.0",
     )
     # Run the tests.
     # NOTE: async rest is not supported against the minimum supported version of google-api-core.