问如何模拟其他方法内部方法调用返回

EN

interface IMethodDescriptorCallerFactory
{
  MethodDescriptorCaller Build(GrpcChannel channel);
}

class MethodDescriptorCallerFactory : IMethodDescriptorCallerFactory
{
  MethodDescriptorCaller Build(GrpcChannel channel)
  {
    return new MethodDescriptorCaller(channel);
  }
}

class Foo
{
  IMethodDescriptorCallerFactory _methodDescriptorCallerFactory;

  public Foo(IMethodDescriptorCallerFactory methodDescriptorCallerFactory)
  {
    _methodDescriptorCallerFactory = methodDescriptorCallerFactory
  }

  public async Task Invoke(HttpContext httpContext)
  {
      GrpcChannel channel = GrpcChannel.ForAddress("address");
      var client = _methodDescriptorCallerFactory.Build(channel);
      client.CallGrpcAsync(); //I need to mock the return of this method
  }
}


class FooTest
{
  [Fact]
  public async Task Test_Invoke()
  {
    var methodDescriptorCaller = Mock.Of<MethodDescriptorCaller>(m =>
        m.CallGrpcAsync() == Task.Completed
    );

    var methodDescriptorCallerFactory = Mock.Of<IMethodDescriptorCallerFactory>(m =>
        m.Build(It.IsAny<GrpcChannel>()) == methodDescriptorCaller
    );

    var foo = new Foo(methodDescriptorCallerFactory);

    var httpContext = Mock.Of<HttpContext>();

    await foo.Invoke(httpContext);

    Mock.Get(methodDescriptorCallerFactory).VerifyAll();
    Mock.Get(methodDescriptorCaller).VerifyAll();
  }
}