「屬性」為 private set 的測試問題

前言

最近同事談到因為 Domain 物件的屬性設定為 private set ，
所以在測試專案中的測試程式要設定該屬性值時，
要透過 Reflection 方式來設定值。
不知大家是否也有類似的問題呢?
private set 的屬性，private 的 method …

討論

屬性會設定成 private set 表示只能在 Class 中設定值，
會這樣設計的原因是不想給外部的 class 來直接設定它。
所以這樣子的屬性值，通常在 constructor 時給值，
或是透過其他的 Public Method 來設定它的值，
以保證整個 Class 的商業邏輯屬性值是合法的。
所以在測試程式時，通常可以透過建立物件時來設定它的值，
或是透過它的 Public Method 來設定。
參考 abp 範例中的 Event Class

public class Event : FullAuditedAggregateRoot<Guid>
{
    public Guid OrganizationId { get; private set; }

    public string UrlCode { get; private set; }

    public string Url { get; private set; }

    public string Title { get; private set; }

    public DateTime StartTime { get; private set; }

    public DateTime EndTime { get; private set; }

    public string Description { get; private set; }

    public bool IsOnline { get; internal set; }

    public string OnlineLink { get; internal set; }

    public Guid? CountryId { get; internal set; }

    public string CountryName { get; internal set; }

    public string City { get; internal set; }

    public string Language { get; set; }

    public int? Capacity { get; internal set; }

    public bool IsRemindingEmailSent { get; set; }

    public bool IsEmailSentToMembers { get; set; }

    public int TimingChangeCount  { get; set; }

    public bool IsTimingChangeEmailSent { get; set; }

    public bool IsDraft { get; private set; }

    public ICollection<Track> Tracks { get; private set; }

    private Event()
    {

    }

    internal Event(
        Guid id,
        Guid organizationId,
        string urlCode,
        string title,
        DateTime startTime,
        DateTime endTime,
        string description)
    : base(id)
    {
        OrganizationId = organizationId;
        UrlCode = Check.NotNullOrWhiteSpace(urlCode, nameof(urlCode), EventConsts.UrlCodeLength, EventConsts.UrlCodeLength);

        SetTitle(title);
        SetDescription(description);
        SetTimeInternal(startTime, endTime);

        Publish(false);

        Tracks = new Collection<Track>();
    }

    public Event SetTitle(string title)
    {
        Title = Check.NotNullOrWhiteSpace(title, nameof(title), EventConsts.MaxTitleLength, EventConsts.MinTitleLength);
        Url = EventUrlHelper.ConvertTitleToUrlPart(Title) + "-" + UrlCode;
        return this;
    }

    public Event SetDescription(string description)
    {
        Description = Check.NotNullOrWhiteSpace(description, nameof(description), EventConsts.MaxDescriptionLength, EventConsts.MinDescriptionLength);
        return this;
    }

    public Event SetTime(DateTime startTime, DateTime endTime)
    {
        if (startTime == StartTime && endTime == EndTime)
        {
            return this;
        }

        if (!IsDraft)
        {
            if (TimingChangeCount >= EventConsts.MaxTimingChangeCountForUser)
            {
                throw new BusinessException(EventHubErrorCodes.CantChangeEventTiming)
                    .WithData("MaxTimingChangeLimit", EventConsts.MaxTimingChangeCountForUser);
            }
        }

        SetTimeInternal(startTime, endTime);

        if (!IsDraft)
        {
            TimingChangeCount++;
            IsTimingChangeEmailSent = false;
        }

        return this;
    }

    private Event SetTimeInternal(DateTime startTime, DateTime endTime)
    {
        if (startTime > endTime)
        {
            throw new BusinessException(EventHubErrorCodes.EndTimeCantBeEarlierThanStartTime);
        }

        StartTime = startTime;
        EndTime = endTime;
        return this;
    }

    internal Event AddTrack(Guid trackId, string name)
    {
        if (Tracks.Any(x => x.Name == name))
        {
            throw new BusinessException(EventHubErrorCodes.TrackNameAlreadyExist)
                .WithData("Name", name);
        }

        Tracks.Add(new Track(trackId, this.Id, name));

        return this;
    }

    public Event UpdateTrack(Guid trackId, string name)
    {
        if (Tracks.Any(x => x.Name == name))
        {
            throw new BusinessException(EventHubErrorCodes.TrackNameAlreadyExist)
                .WithData("Name", name);
        }

        var track = Tracks.SingleOrDefault(x => x.Id == trackId);
        if (track is null)
        {
            throw new BusinessException(EventHubErrorCodes.TrackNotFound);
        }

        track.SetName(name);

        return this;
    }

    public Event RemoveTrack(Guid trackId)
    {
        var track = Tracks.SingleOrDefault(x => x.Id == trackId);
        if (track is null)
        {
            throw new BusinessException(EventHubErrorCodes.TrackNotFound);
        }

        Tracks.Remove(track);

        return this;
    }

    public Event AddSession(
        Guid trackId,
        Guid sessionId,
        string title,
        string description,
        DateTime startTime,
        DateTime endTime,
        string language,
        ICollection<Guid> speakerUserIds)
    {
        CheckIfValidSessionTime(startTime, endTime);

        var track = GetTrack(trackId);
        track.AddSession(sessionId, title, description,startTime, endTime, language, speakerUserIds);
        return this;
    }

    public Event UpdateSession(
        Guid trackId,
        Guid sessionId,
        string title,
        string description,
        DateTime startTime,
        DateTime endTime,
        string language,
        ICollection<Guid> speakerUserIds)
    {
        CheckIfValidSessionTime(startTime, endTime);

        var track = GetTrack(trackId);
        track.UpdateSession(sessionId, title, description, startTime, endTime, language, speakerUserIds);
        return this;
    }

    public Event RemoveSession(Guid trackId, Guid sessionId)
    {
        var track = Tracks.SingleOrDefault(x => x.Id == trackId);
        if (track is null)
        {
            throw new BusinessException(EventHubErrorCodes.TrackNotFound);
        }

        track.RemoveSession(sessionId);

        return this;
    }

    public Event Publish(bool isPublish = true)
    {
        IsDraft = !isPublish;

        return this;
    }

    public bool IsLive(DateTime now)
    {
        return now.IsBetween(StartTime, EndTime);
    }

    private Track GetTrack(Guid trackId)
    {
        return Tracks.FirstOrDefault(t => t.Id == trackId) ??
                throw new EntityNotFoundException(typeof(Track), trackId);
    }

    private void CheckIfValidSessionTime(DateTime startTime, DateTime endTime)
    {
        if (startTime < this.StartTime || this.EndTime < endTime)
        {
            throw new BusinessException(EventHubErrorCodes.SessionTimeShouldBeInTheEventTime);
        }
    }
}

像上述的 Description 屬性，
可透過 Constructor 來設定值，或是透過 public 的 SetDescription Method 來設定。
那這樣來看，不需要在測試程式中需要使用 Reflection 的方式來設定物件的屬性值。
所以要好好地檢視一下物件的設計，是否真的需要使用 private set ，
還是使用 internal set 就可以達到我們的目的呢?
例如透過同一個專案中的 Manager 來操作它們(請參考EventManager Class)
而那些 private Method ，是否也可以用 internal 呢?
還是其實應該會有一個 public method 可以來做這些事呢?

參考資料

存取修飾詞
abpframework/eventhub