Add basic test for each generated client method

Author: lidizheng

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

@@ -4,6 +4,7 @@
 import mock
 
 import grpc
+from grpc.experimental import aio
 import math
 import pytest
 
@@ -17,6 +18,7 @@ from {{ (api.naming.module_namespace + (api.naming.versioned_module_name,) + ser
 from {{ (api.naming.module_namespace + (api.naming.versioned_module_name,) + service.meta.address.subpackage)|join(".") }}.services.{{ service.name|snake_case }} import transports
 from google.api_core import client_options
 from google.api_core import grpc_helpers
+from google.api_core import grpc_helpers_async
 {% if service.has_lro -%}
 from google.api_core import future
 from google.api_core import operations_v1
@@ -213,6 +215,89 @@ def test_{{ method.name|snake_case }}(transport: str = 'grpc'):
     {% endfor %}
     {% endif %}
 
+
+@pytest.mark.asyncio
+async def test_{{ method.name|snake_case }}_async(transport: str = 'grpc_asyncio'):
+    client = {{ service.async_client_name }}(
+        credentials=credentials.AnonymousCredentials(),
+        transport=transport,
+    )
+
+    # Everything is optional in proto3 as far as the runtime is concerned,
+    # and we are mocking out the actual API, so just send an empty request.
+    request = {{ method.input.ident }}()
+    {% if method.client_streaming %}
+    requests = [request]
+    {% endif %}
+
+    # Mock the actual call within the gRPC stub, and fake the request.
+    with mock.patch.object(
+            type(client._client._transport.{{ method.name|snake_case }}),
+            '__call__') as call:
+        # Designate an appropriate return value for the call.
+        {% if method.void -%}
+        call.return_value = grpc_helpers_async.FakeUnaryUnaryCall(None)
+        {% elif method.lro -%}
+        call.return_value = grpc_helpers_async.FakeUnaryUnaryCall(
+            operations_pb2.Operation(name='operations/spam')
+        )
+        {% elif not method.client_streaming and method.server_streaming -%}
+        call.return_value = mock.Mock(aio.UnaryStreamCall, autospec=True)
+        call.return_value.read = mock.AsyncMock(side_effect=[{{ method.output.ident }}()])
+        {% elif method.client_streaming and method.server_streaming -%}
+        call.return_value = mock.Mock(aio.StreamStreamCall, autospec=True)
+        call.return_value.read = mock.AsyncMock(side_effect=[{{ method.output.ident }}()])
+        {% else -%}
+        call.return_value ={{' '}}
+            {%- if not method.client_streaming and not method.server_streaming -%}
+                grpc_helpers_async.FakeUnaryUnaryCall
+            {%- else -%}
+                grpc_helpers_async.FakeStreamUnaryCall
+            {%- endif -%}({{ method.output.ident }}(
+            {%- for field in method.output.fields.values() | rejectattr('message') %}
+            {{ field.name }}={{ field.mock_value }},
+            {%- endfor %}
+        ))
+        {% endif -%}
+        {% if method.client_streaming and method.server_streaming %}
+        response = await client.{{ method.name|snake_case }}(iter(requests))
+        {% elif method.client_streaming and not method.server_streaming %}
+        response = await (await client.{{ method.name|snake_case }}(iter(requests)))
+        {% else %}
+        response = await client.{{ method.name|snake_case }}(request)
+        {% endif %}
+
+        # Establish that the underlying gRPC stub method was called.
+        assert len(call.mock_calls)
+        _, args, _ = call.mock_calls[0]
+        {% if method.client_streaming %}
+        assert next(args[0]) == request
+        {% else %}
+        assert args[0] == request
+        {% endif %}
+
+    # Establish that the response is the type that we expect.
+    {% if method.void -%}
+    assert response is None
+    {% elif method.lro -%}
+    assert isinstance(response, future.Future)
+    {% elif method.server_streaming -%}
+    message = await response.read()
+    assert isinstance(message, {{ method.output.ident }})
+    {% else -%}
+    assert isinstance(response, {{ method.client_output_async.ident }})
+    {% for field in method.output.fields.values() | rejectattr('message') -%}
+    {% if field.field_pb.type in [1, 2] -%} {# Use approx eq for floats -#}
+    assert math.isclose(response.{{ field.name }}, {{ field.mock_value }}, rel_tol=1e-6)
+    {% elif field.field_pb.type == 8 -%} {# Use 'is' for bools #}
+    assert response.{{ field.name }} is {{ field.mock_value }}
+    {% else -%}
+    assert response.{{ field.name }} == {{ field.mock_value }}
+    {% endif -%}
+    {% endfor %}
+    {% endif %}
+
+
 {% if method.field_headers %}
 def test_{{ method.name|snake_case }}_field_headers():
     client = {{ service.client_name }}(