Было.cs

        protected static bool IsListSuitableForSimpleAdmin(IList<Record> records)
        {
            bool returnValue = false;
            if (records != null)
            {
                int sundayCount = 0;
                int mondayCount = 0;
                int tuesdayCount = 0;
                int wednesdayCount = 0;
                int thursdayCount = 0;
                int fridayCount = 0;
                int saturdayCount = 0;
                foreach (Record in records)
                {
                    switch (record.DayOfWeek)
                    {
                        case DayOfWeek.Sunday:
                            sundayCount++;
                            break;
                        case DayOfWeek.Monday:
                            mondayCount++;
                            break;
                        case DayOfWeek.Tuesday:
                            tuesdayCount++;
                            break;
                        case DayOfWeek.Wednesday:
                            wednesdayCount++;
                            break;
                        case DayOfWeek.Thursday:
                            thursdayCount++;
                            break;
                        case DayOfWeek.Friday:
                            fridayCount++;
                            break;
                        case DayOfWeek.Saturday:
                            saturdayCount++;
                            break;
                    }

                }
                returnValue = (sundayCount == 1 &
                                   mondayCount == 1 &
                                   tuesdayCount == 1 &
                                   wednesdayCount == 1 &
                                   thursdayCount == 1 &
                                   fridayCount == 1 &
                                   saturdayCount == 1);
            }
            return returnValue;
        }

Стало.cs

        protected static bool IsListSuitableForSimpleAdmin(IList<Record> records)
        {
            var byDayCounts = (records ?? Enumerable.Empty<Record>())
                .GroupBy(record => record.DayOfWeek)
                .Select(byDays => byDays.Count())
                .ToList();

            return byDayCounts.All(count => count == 1) && byDayCounts.Count == 7;
        }