public static class DateTimeAssert
{
    public static void AreEqual(DateTime? expectedDate, DateTime? actualDate, DateTimeDeltaType deltaType, int count)
    {
        if (expectedDate == null && actualDate == null)
        {
            return;
        }
        else if (expectedDate == null)
        {
            throw new NullReferenceException("The expected date was null");
        }
        else if (actualDate == null)
        {
            throw new NullReferenceException("The actual date was null");
        }
        TimeSpan expectedDelta = GetTimeSpanDeltaByType(deltaType, count);
        double totalSecondsDifference = Math.Abs(((DateTime)actualDate - (DateTime)expectedDate).TotalSeconds);

        if (totalSecondsDifference > expectedDelta.TotalSeconds)
        {
            throw new Exception(string.Format("Expected Date: {0}, Actual Date: {1} \nExpected Delta: {2}, Actual Delta in seconds- {3} (Delta Type: {4})",
                                            expectedDate,
                                            actualDate,
                                            expectedDelta,
                                            totalSecondsDifference,
                                            deltaType));
        }
    }

    private static TimeSpan GetTimeSpanDeltaByType(DateTimeDeltaType type, int count)
    {
        TimeSpan result = default(TimeSpan);

        switch (type)
        {
            case DateTimeDeltaType.Days:
                result = new TimeSpan(count, 0, 0, 0);
                break;
            case DateTimeDeltaType.Minutes:
                result = new TimeSpan(0, count, 0);
                break;
            default: throw new NotImplementedException("The delta type is not implemented.");
        }

        return result;
    }
}