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());
}