public void LastColumnUsed()
{
IXLWorksheet ws = new XLWorkbook().AddWorksheet("Sheet1");
ws.Cell("A1").Value = "A1";
ws.Cell("B1").Value = "B1";
ws.Cell("A2").Value = "A2";
var lastCoUsed = ws.LastColumnUsed().ColumnNumber();
Assert.AreEqual(2, lastCoUsed);
}