HttpContext.Current is always null in unit tests [duplicate]

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• Setting HttpContext.Current.Session in a unit test 14 answers

I have unit tests which uses following extension method

CSVExtensions.CreateCSVFile(fileName, data);

Now during testing

public static class CSVExtension{
    public static void CreateCSVFile(string filename, byte[] bytes)
    {
        HttpContext.Current.Response.Clear();
        HttpContext.Current.Response.ContentType = "text/csv";
        HttpContext.Current.Response.AddHeader("Content-Length", bytes.Length.ToString());
        HttpContext.Current.Response.AddHeader("Content-disposition", "attachment; filename=\"" + filename + ".csv" + "\"");
        HttpContext.Current.Response.BinaryWrite(bytes);
        HttpContext.Current.Response.Flush();
        HttpContext.Current.Response.End();
    }

HttpContext.Current is always null

Please suggest solution