public void ExportCategoriesToXlsx_ReturnFilledStreamWithCorrecctStructure() { var categories = new List <Category>() { new Category { Id = "id1", Name = "name1" }, new Category { Id = "id2", Name = "name2" } }; var result = _exportManager.ExportCategoriesToXlsx(categories); Assert.IsTrue(result.Length > 0); using (var ms = new MemoryStream(result)) { XSSFWorkbook s = new XSSFWorkbook(ms); var sheet = s.GetSheet("Category"); var row1 = sheet.GetRow(0); var row2 = sheet.GetRow(1); var row3 = sheet.GetRow(2); Assert.IsNotNull(sheet); Assert.IsNotNull(row1); Assert.IsNotNull(row2); //row1 should contains header- property name Assert.AreEqual(row1.GetCell(0).StringCellValue, "Id"); Assert.AreEqual(row1.GetCell(1).StringCellValue, "Name"); Assert.AreEqual(row2.GetCell(0).StringCellValue, "id1"); Assert.AreEqual(row2.GetCell(1).StringCellValue, "name1"); Assert.AreEqual(row3.GetCell(0).StringCellValue, "id2"); Assert.AreEqual(row3.GetCell(1).StringCellValue, "name2"); } }