public void ExportBrandsToXlsx_ReturnFilledStreamWithCorrecctStructure() { var brands = new List <Brand>() { new Brand() { Id = "id1", Name = "brand1" }, new Brand() { Id = "id2", Name = "brand2" } }; var result = _exportManager.ExportBrandsToXlsx(brands); Assert.IsTrue(result.Length > 0); using (var ms = new MemoryStream(result)) { XSSFWorkbook s = new XSSFWorkbook(ms); var sheet = s.GetSheet("Brand"); var row1 = sheet.GetRow(0); var row2 = sheet.GetRow(1); Assert.IsNotNull(sheet); Assert.IsNotNull(row1); Assert.IsNotNull(row2); //row1 should contains header- property name Assert.AreEqual(row1.GetCell(0).StringCellValue, "Id"); Assert.AreEqual(row2.GetCell(0).StringCellValue, "id1"); } }