Best Practices Testing gRPC Services

[dwhu]

Advice on Testing gRPC Clients

grpc: ^3.0.0

Repro steps

1. I want to create a set of tests that verify that data is being passed correctly to gRPC service. Currently the service is mocked out with Mocktail and the test looks like the following:

  class MockServiceClient extends Mock
      implements service_proto.ServiceClient {}

  class MockCreateRequest extends Mock implements service_proto.CreateRequest {}

  class MockCreateResponse extends Fake
      implements ResponseFuture<service_proto.CreateResponse> {}
  ...
   setUpAll(() {
      registerFallbackValue(MockCreateRequest());
      registerFallbackValue<ResponseFuture<service_proto.Response>>(MockCreateResponse());
    });

    setUp(() {
      serviceClient = MockServiceClient();
      authnRepository = AuthnRepository(
        serviceClient,
      );
    });
  ...
    group('signUp', () {
      setUp(() {
        when(
          () => dealerServiceClient.create(any()),
        ).thenAnswer((_) => MockCreateResponse());
      });

      test('calls create', () async {
        await authnRepository.signUp(
            givenName: givenName,
            familyName: familyName,
            email: email,
            password: password);
        verify(() =>
            dealerServiceClient.create(service_proto.CreateRequest()
              ..displayName = dealerName
              ..adminGivenName = givenName
              ..adminFamilyName = familyName
              ..adminEmailAddress = email
              ..adminPassword = password)).called(1);
      });
      ...
  });

Expected result: I would expect this test to work since I'm mocking out ResponseFuture

Actual result:

I continue to run into issues mocking or faking out ResponseFuture because it doesn't conform to the Future interface.

Error: The argument type 'Future<CreateResponse>' can't be assigned to the parameter
type 'ResponseFuture<CreateResponse>'.
 - 'Future' is from 'dart:async'.
 - 'Dealer' is from 'package:proto/service/v1/service.pb.dart' ('lib/proto/service/v1/service.pb.dart').
 - 'ResponseFuture' is from 'package:grpc/src/client/common.dart'

or even

package:test_api                                        Fake.noSuchMethod
package:async/src/delegate/future.dart 32:13            MockCreateResponse.then
dart:async                                              _awaitHelper
package:auth/repo/authn_repository.dart 79:7   AuthnRepository.signUp
test/authn_repo/repo/authn_repository_test.dart 123:31  main.<fn>.<fn>.<fn>
test/authn_repo/repo/authn_repository_test.dart 122:34  main.<fn>.<fn>.<fn>

UnimplementedError: then

Questions

1. Is there a better way for me to write this test? Is mocking the right thing to do? Or is there a better way to fake the service?
2. If mocking is the correct approach, how can I get grpc-dart and the mocking framework to play nicely with each-other?

If there is a recommended approach, I'm happy to contribute some docs on best practices here.

Appreciate the help & keep up the great work!

[mraleph]

My preference would be to just setup an actual mock backend (which is rather simple to achieve using server part of the grpc package) instead of mocking the service class itself.

[enyo]

@mraleph would you mind elaborating on that a bit? So you mean to actually setup a server that you then run and that responds to the requests?

[mraleph]

@enyo yep, exactly. if you want to test client logic then setup a mock server (with test mock services) that responds to requests from the client you want to test.