public void TestMethod_Test() { var excelTemplate = JsonConvert.DeserializeObject <ExcelTemplate>(_testJson); IExcelExport jsonToExcel = new ExcelExport(); var byteTask = jsonToExcel.ConvertJsonToExcelAsync(excelTemplate); byteTask.Wait(); using (MemoryStream memStream = new MemoryStream(byteTask.Result)) using (FileStream stream = new FileStream(@"C:\Temp\Test.xls", FileMode.Create, FileAccess.Write)) { memStream.WriteTo(stream); } }