NSubstitute mock generic method

Question

I have the following method signature in an interface:

public interface ISettingsUtil
{
    T GetConfig<T>(string setting, dynamic settings);
}

Which I have attempted to mock:

var settingsUtil = Substitute.For<ISettingsUtil>();
var maxImageSize = settingsUtil.GetConfig<long>("maxImageSize", 
                                              Arg.Any<dynamic>()).Returns(100L);

This throws a Microsoft.CSharp.RuntimeBinder.RuntimeBinderException exception on the 2nd line:

'long' does not contain a definition for 'Returns'

Any thoughts on how to mock T GetConfig<T>(string setting, dynamic settings) correctly?

Answer 1

NSubstitute does not work with members that use dynamic. (Github issue)

Answer 2

For anyone still struggling with this, you can actually mock dynamics in NSubsitute, it just requires jumping through some minor hoops. See the below case of mocking out calls to a signalR client hub.

The important line is this one:

SubstituteExtensions.Returns(_hubContext.Clients.All, _mockClient);

In order to mock the dynamic I have created an interface with the methods I want to listen for. You then need to use SubstituteExtensions.Returns rather than simply chaining a .Returns at the end of the object.
If you don't need to verify anything you could also use an anonymous object.

Full code sample follows:

[TestFixture]
public class FooHubFixture
{
    private IConnectionManager _connectionManager;
    private IHubContext _hubContext;
    private IMockClient _mockClient;

    [SetUp]
    public void SetUp()
    {
        _hubContext = Substitute.For<IHubContext>();
        _connectionManager = Substitute.For<IConnectionManager>();

        _connectionManager.GetHubContext<FooHub>().Returns(_hubContext);
        _mockClient = Substitute.For<IMockClient>();
        SubstituteExtensions.Returns(_hubContext.Clients.All, _mockClient);
    }

    [Test]
    public void PushFooUpdateToHub_CallsUpdateFooOnHubClients()
    {
        var fooDto = new FooDto();
        var hub = new FooHub(_connectionManager);
        hub.PushFooUpdateToHub(fooDto);
        _mockClient.Received().updateFoo(fooDto);
    }

    public interface IMockClient
    {
        void updateFoo(object val);
    }
}



public class FooHub : Hub
    {
        private readonly IConnectionManager _connectionManager;

        public FooHub(IConnectionManager connectionManager)
        {
            _connectionManager = connectionManager;
        }

        public void PushFooUpdateToHub(FooDto fooDto)
        {
            var context = _connectionManager.GetHubContext<FooHub>();
            context.Clients.All.updateFoo(fooDto);
        }
    }