public class AnalyticsService{

  IDateTimeProvider _dateTimeProvider;

  public AnalyticsService(IDateTimeProvider dateTimeProvider){
    _dateTimeProvider = dateTimeProvider
  }

  public int GetCountAndSave(){
    var sessions = GoogleService.GetSessions();
    var saveCount = 0;
    if (_dateTimeProvider.DayOfWeek() == DayOfWeek.Friday)
    {
        saveCount = AddToData(sessions);
    }
    else
    {
        Console.WriteLine("Not Today!");
    }
    return saveCount;
  }
}

public interface IDateTimeProvider
{
    DayOfWeek DayOfWeek();
}

public class DateTimeProvider : IDateTimeProvider
{
    public DayOfWeek DayOfWeek()
    {
        return DateTime.Today.DayOfWeek;
    }
}