public void TestCreateSheet()
        {
            string dataFilePath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "file", "nothisfile.xlsx");
            NPOIOperator oper = new NPOIOperator(dataFilePath, true);

            var firstSheet = oper.CreateSheet("FirstSheet");
            Assert.IsNotNull(firstSheet);

            var secondSheet = oper.CreateSheet("SecondSheet");
            Assert.IsNotNull(secondSheet);

            Assert.AreEqual(2, oper.GetSheetCount());
        }