How can I Unit Test using mock with EPPlus?

Question

I'm using EPPLus for a project, and I'm trying to just create an Excel Worksheet in memory to mock it.

the class I'm using for unit testing has a method

public ExcelPackage GetExcelPackage()
{
    using (var package = new ExcelPackage())
    {
        ExcelWorksheet returnWorksheet = package.Workbook.Worksheets.Add("worksheet");
        returnWorksheet.Cells[1, 1].Value = "043";
        returnWorksheet.Cells[1, 2].Value = "21677";
        returnWorksheet.Cells[1, 3].Value = "100";
        returnWorksheet.Cells[1, 4].Value = String.Empty;
        returnWorksheet.Cells[1, 5].Value = "12292016";
        returnWorksheet.Cells[1, 6].Value = String.Empty;
        return package;
    }
}

In my InputFileController, I get a null object error when I call package.Workbook.Worksheets.First.

public static IInputFileRepository ReadExcelFile(IFileDataSource excelFileDataSource)
    {
        FileInfo fileToRead = new FileInfo(excelFileDataSource.InputFile);
        List<string> lines = new List<string>();
        ExcelPackage package = excelFileDataSource.GetExcelPackage();
        ExcelWorksheet worksheet = package.Workbook.Worksheets.First();

Any idea what I could be doing wrong?

Answer 1

So, it looks like I had an unrelated bug. Rather than having my IFileDataSource return an ExcelPackage, I have it return the filename, and use EPPlus to open and read that file from my InputController.

 public static IInputFileRepository ReadExcelFile(IFileDataSource excelFileDataSource)
    {
        FileInfo fileToRead = new FileInfo(excelFileDataSource.InputFile);
        List<string> lines = new List<string>();
        var fileInfo = new FileInfo(excelFileDataSource.InputFile);
        using (var package = new ExcelPackage(newFile: fileInfo))
        {
            ExcelWorksheet worksheet = package.Workbook.Worksheets.First();
            for (int rowIndex = 2; rowIndex <= worksheet.Dimension.End.Row; rowIndex++)

Answer 2

Null reference error happens due to disposing of the object - which is due to the using statement around the code block.

I'm putting my answer here in case anybody comes and wonders about the root cause.