Question

I’m novice in unit testing field, so I have some questions:

Is it a good practice to make method that returns a DataTable? If yes, how could I test it then?

This is a function that they ask me to test:

public static DataTable GeneratePeriods(DateTime startDate, DateTime endDate, string periodicity)
{
    try
    {
        using (DataTable periods = new DataTable())
        {
            periods.Columns.Add(new DataColumn("Dates", typeof(DateTime)));
            int startYear = startDate.Year;
            int endYear = endDate.Year;
            int Diff = endYear - startYear + 1;
            int LoopYear;
            /* This generates all regular periods from the begin date to the end date */
            switch (periodicity)
            {
                //monthly
                case "Mensuelle":
                    for (int j = 0; j < Diff; j++)
                    {
                        LoopYear = startYear + j;
                        for (int i = 1; i <= 12; i++)
                            if (i != 12)
                                periods.Rows.Add(new DateTime(LoopYear, i + 1, 1).AddDays(-1));
                            else
                                periods.Rows.Add(new DateTime(LoopYear, 12, 31));
                    }
                    break;
                //quarterly
                case "Trimestrielle":
                    for (int j = 0; j < Diff; j++)
                    {
                        LoopYear = startYear + j;
                        for (int i = 1; i <= 4; i++)
                            if (i != 4)
                                periods.Rows.Add(new DateTime(LoopYear, (i * 3) + 1, 1).AddDays(-1));
                            else
                                periods.Rows.Add(new DateTime(LoopYear, 12, 31));
                    }
                    break;
                //biannual
                case "Semestrielle":
                    for (int j = 0; j < Diff; j++)
                    {
                        LoopYear = startYear + j;
                        for (int i = 1; i <= 2; i++)
                            if (i != 2)
                                periods.Rows.Add(new DateTime(LoopYear, (i * 6) + 1, 1).AddDays(-1));
                            else
                                periods.Rows.Add(new DateTime(LoopYear, 12, 31));
                    }
                    break;
                //annual
                case "Annuelle":
                    for (int j = 0; j < Diff; j++)
                    {
                        LoopYear = startYear + j;
                        for (int i = 1; i <= 1; i++)
                            periods.Rows.Add(new DateTime(LoopYear, 12, 31));
                    }
                    break;
            }
            //this adds startDate in periods datatable if it doesn't exist
            if (periods.Select(String.Format("Dates = '{0}'", startDate)).Length == 0)
                periods.Rows.Add(startDate);
            //this adds endDate date in periods datatable if it doesn't exist
            if (periods.Select(String.Format("Dates = '{0}'", endDate.AddDays(-1))).Length == 0)
                periods.Rows.Add(endDate);
            //this removes all date ranges below the startDate
            DataRow[] dr = periods.Select(String.Format("Dates < '{0}'", startDate));
            foreach (DataRow row in dr)
                periods.Rows.Remove(row);
            //this removes all date ranges above the endDate
            DataRow[] dr1 = periods.Select(String.Format("Dates >'{0}'", endDate.AddDays(-1)));
            foreach (DataRow row in dr1)
                periods.Rows.Remove(row);
            //this adds endDate date in periods datatable if it doesn't exist for the second time ! (I personnaly don't know why it's duplicated but it dosen't work without this =) )
            if (periods.Select(String.Format("Dates = '{0}'", endDate.AddDays(-1))).Length == 0)
                periods.Rows.Add(endDate);
            DataView dv = new DataView(periods) { Sort = "Dates ASC" };
            // this initialize a new datatable with sorted dates
            DataTable dt_dates = dv.ToTable();
            // this initialize a new datatable 
            DataTable dt_periods = new DataTable();
            dt_periods.Columns.Add("Periods", typeof(string));
            dt_periods.Columns.Add("NombreJours", typeof(int));
            // this loop creates period ranges shown to the user (Du startDate au endDate)
            DateTime dateDebutPeriode;
            DateTime dateFinPeriode;
            int NombreJours;
            for (int i = 0; i < dv.Table.Rows.Count - 1; i++)
                if (i == 0)
                {
                    dateDebutPeriode = DateTime.Parse(dt_dates.Rows[i]["Dates"].ToString());
                    dateFinPeriode = DateTime.Parse(dt_dates.Rows[i + 1]["Dates"].ToString());
                    NombreJours = dateFinPeriode.Subtract(dateDebutPeriode).Days + 1;
                    dt_periods.Rows.Add(String.Format("Du {0} au {1}", dateDebutPeriode.ToShortDateString(), dateFinPeriode.ToShortDateString()), NombreJours);
                }
                else
                    if (i == dv.Table.Rows.Count - 2)
                    {
                        dateDebutPeriode = DateTime.Parse(dt_dates.Rows[i]["Dates"].ToString()).AddDays(1);
                        dateFinPeriode = DateTime.Parse(dt_dates.Rows[i + 1]["Dates"].ToString()).AddDays(-1);
                        NombreJours = dateFinPeriode.Subtract(dateDebutPeriode).Days + 1;
                        dt_periods.Rows.Add(String.Format("Du {0} au {1}", dateDebutPeriode.ToShortDateString(), dateFinPeriode.ToShortDateString()), NombreJours);
                    }
                    else
                    {
                        dateDebutPeriode = DateTime.Parse(dt_dates.Rows[i]["Dates"].ToString()).AddDays(1);
                        dateFinPeriode = DateTime.Parse(dt_dates.Rows[i + 1]["Dates"].ToString());
                        NombreJours = dateFinPeriode.Subtract(dateDebutPeriode).Days + 1;
                        dt_periods.Rows.Add(String.Format("Du {0} au {1}", dateDebutPeriode.ToShortDateString(), dateFinPeriode.ToShortDateString()), NombreJours);
                    }
            return dt_periods;
        }
    }
    catch (InvalidOperationException)
    {
        throw;
    }
}

Answer 1

What you can test here, is whether returned DataTable structure is indeed what you expect. Those are plain and simple unit tests. Determine what is expected from GeneratePeriods method (as in, what do you want it to do?), and write tests checking that it is in fact what method does. For example:

• test whether correct number of periods was generated
• test whether given period has correctly set rows/columns
• test whether row data is in correct format
• …and probably lot more

On a side note, there’s nothing wrong with returning DataTable from function.