UnitTestViewModel.cs

public class UnitTestViewModel
{
    public Command LoadDataCommand { get; set; }
    public string Data { get; set; }

    public UnitTestViewModel()
    {
        LoadDataCommand = new Command(async () => await LoadData());
    }

    public async Task LoadData()
    {
        Data = await DependencyService.Get<IDeliverServerSideData>().GetJsonData();
    }
}