public void CommandBus_Should_Throw_NotImplementedException_If_Handler_Not_Found() { // Arrange var resolver = new Mock <IResolver>(); var command = this.random.Create <SampleCommand>(); var bus = new CommandBus(resolver.Object); void action(CommandBus c) => c.Send(command); // Action && Assert bus.Invoking(action).Should() .Throw <NotImplementedException>() .WithMessage($"Handler not found for command '{command.GetType().Name}'"); }