Generated unit test has NameError if response contains imported message in oneof

[dizcology]

To reproduce, add a fragment file:

# In tests/fragments/broken.proto

syntax = "proto3";

package google.fragment;

import "google/api/client.proto";
import "import.proto";

service MyService {
  option (google.api.default_host) = "my.example.com";
  rpc MyMethod(MethodRequest) returns (MethodResponse) {}
}

message MethodRequest {
  string input = 1;
}

message Container {
  Import import = 1;
}

message MethodResponse {
  oneof data {
    Container container = 1;
  }
}

Then run nox -s fragment-3.7 -- tests/fragments/broken.proto. The generated unit test fails with NameError: name 'import_' is not defined.

Some variants of similar protos do not fail:

1. If oneof is removed.
2. If Container container = 1; is replaced with just Import import = 1;.
3. If Import import = 1; is replaced with a field of primitive data type, e.g. string import = 1;.
4. If MethodResponse is empty, and the oneof is moved into MethodRequest. (This seems to be incidental to the implementation of unit test generation.)

Two pieces of generator code are relevant here:

1. Import statements https://github.com/googleapis/gapic-generator-python/blob/v1.10.0/gapic/schema/wrappers.py#L1489: This populates the types referenced in a method, _ref_types. It is used in the template to add import statements: https://github.com/googleapis/gapic-generator-python/blob/v1.10.0/gapic/templates/tests/unit/gapic/%25name_%25version/%25sub/test_%25service.py.j2#L65
2. Response https://github.com/googleapis/gapic-generator-python/blob/v1.10.0/gapic/schema/wrappers.py#L176: This recursively populates a mock message. It is used in the template for call.return_value: https://github.com/googleapis/gapic-generator-python/blob/v1.10.0/gapic/templates/tests/unit/gapic/%25name_%25version/%25sub/test_macros.j2#L35

In the example above, it seems that the response message was properly populated with import_.Import(...) within its container field, but the method's _ref_types attribute did not include import_.

[dizcology]

The unit tests' response messages should only be populated with fields which are not messages through rejectattr('message') in https://github.com/googleapis/gapic-generator-python/blob/v1.10.0/gapic/templates/tests/unit/gapic/%25name_%25version/%25sub/test_macros.j2#L33. But in the example fragment above, sub-messages are populated as well, causing the error:

@pytest.mark.parametrize("request_type", [
  test_oneof_imported_response.MethodRequest,
  dict,
])
def test_my_method(request_type, transport: str = 'grpc'):
    client = MyServiceClient(
        credentials=ga_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 = request_type()

    # Mock the actual call within the gRPC stub, and fake the request.
    with mock.patch.object(
            type(client.transport.my_method),
            '__call__') as call:
        # Designate an appropriate return value for the call.
        call.return_value = test_oneof_imported_response.MethodResponse(
            container=test_oneof_imported_response.Container(import_=import_.Import(path='path_value')),
        )
        response = client.my_method(request)

        # Establish that the underlying gRPC stub method was called.
        assert len(call.mock_calls) == 1
        _, args, _ = call.mock_calls[0]
        assert args[0] == test_oneof_imported_response.MethodRequest()

    # Establish that the response is the type that we expect.
    assert isinstance(response, test_oneof_imported_response.MethodResponse)

[dizcology]

The issue is actually the second for-loop https://github.com/googleapis/gapic-generator-python/blob/main/gapic/templates/tests/unit/gapic/%25name_%25version/%25sub/test_macros.j2#L38, where the first oneof field is populated even if it a message, a different behavior than the first, non-oneof, for-loop.