靜態元素 (Static Elements) 的單元測試, 以 System.IO.File.ReadAllText 為例

Unit Test for Static Elements (System.IO.File.ReadAllText) in ASP.NET Core 6 MVC

前言

接續前一篇樂透開獎(含日期限制) 的例子, 假設有一個新的需求: "樂透開奬有一個前置作業, 必須由主辦人員按下[開始]按鈕, 才能開獎".

本文假設主辦人員按下[開始]按鈕, 會在主機端產生一個檔案 (Extras/startup.txt), 內含主辦人員的姓名.

因此, 程式要增加一個讀取檔案內容的動作.

若可讀到 Extras/startup.txt, 才可開獎, 並回傳開獎的結果, 要再加上主辦人員的姓名.
若讀不到 Extras/startup.txt, 則不可開獎, 並回傳警告訊息.
- "", -2, "主辦人員尚未按下[開始]按鈕". // 第1個空字串, 代表主辦人員的姓名

這裡很單純的想法, 是用 File.ReadAllText() 的方法, 因為是 static class + static method, 應該要如何建立測試呢?

以下係採參考文件1..及2.. 方式進行演練及實作.

完整範例可由 GitHub 下載.

演練細節

步驟_1: 安裝以下套件

TestableIO.System.IO.Abstractions.Wrappers 20.0.4:
- 用以將 System.IO 的類別, 以 interface 的方式進行打包. 以 System.IO.File 為例, 會有 IFile 介面及 FileWrapper 類別.
TestableIO.System.IO.Abstractions.TestingHelpers 20.0.4
- 主要有一些現成的 mock 類別, 以利測試之用.

步驟_2: 將 IFileSystem 註冊至 DI container

#region 註冊相關的服務
builder.Services.AddSingleton<IRandomGenerator, RandomGenerator>();
builder.Services.AddScoped<ILottoService, LottoService>();
builder.Services.AddSingleton<IDateTimeProvider, DateTimeProvider>();
builder.Services.AddSingleton<IFileSystem, FileSystem>();
#endregion

步驟_3: 修改 LottoService 的處理邏輯

1.. 修改建構子, 加入 IFileSystem 物件的注入.

private readonly IRandomGenerator _randomGenerator;
private readonly IDateTimeProvider _dateTimeProvider;
private readonly IFileSystem _fileSystem;

public LottoService(IRandomGenerator randomGenerator, IDateTimeProvider dateTimeProvider, IFileSystem fileSystem) 
{
    _randomGenerator = randomGenerator;
    _dateTimeProvider = dateTimeProvider;
    _fileSystem = fileSystem;
}

2.. 修改 Lottoing() 方法, 加入 Extra/startup.txt 的檢查.

public LottoViewModel Lottoing(int min, int max)
{

    var result = new LottoViewModel();

    // -----------------------
    // 檢核1: 是否為每個月 5 日
    // -----------------------
    var now = _dateTimeProvider.GetCurrentTime();
    if (now.Day != 5)
    {
        result.Sponsor = string.Empty;
        result.YourNumber = -1;
        result.Message = "非每個月5日, 不開獎";
        return result;
    }

    // -----------------------
    // 檢核2: 主辦人員是否已按下[開始]按鈕
    // -----------------------
    // 註: 這裡有可能會出現一些 Exception, 例如: FileNotFoundException
    var sponsor = string.Empty;
    try
    {
        sponsor = _fileSystem.File.ReadAllText("Extras/startup.txt");
    }
    catch (Exception)
    {
        result.Sponsor = sponsor;
        result.YourNumber = -2;
        result.Message = "主辦人員尚未按下[開始]按鈕";
        return result;
    }

    // Random(min, max): 含下界, 不含上界
    var yourNumber = _randomGenerator.Next(min, max);
    // 只要餘數是 9, 就代表中獎
    var message = (yourNumber % 10 == 9) ? "恭喜中獎" : "再接再厲";
    result.Sponsor = sponsor;
    result.YourNumber = yourNumber;
    result.Message = message;

    return result;
}

步驟_4: 修改原有的測試案例

1.. 因為 LottoService 的建構子增加了 IFileSystem 這個參數, 所以, 原有的測試案例, 也要跟著改, 不然會編譯失敗.

[TestMethod()]
public void Test_Lottoing_今天是20240105_主辦人宣告開始_輸入亂數範圍_0_10_預期回傳_9_恭喜中獎()
{
    // Arrange
    var expected = new LottoViewModel()
    { Sponsor = "傑士伯", YourNumber = 9, Message = "恭喜中獎" }
                .ToExpectedObject();

    int fixedValue = 9;
    DateTime today = new(2024, 01, 05);
    var mockRandomGenerator = new Mock<IRandomGenerator>();
    var mockDateTimeProvider = new Mock<IDateTimeProvider>();
    mockRandomGenerator.Setup(r => r.Next(It.IsAny<int>(), It.IsAny<int>())).Returns(fixedValue);
    mockDateTimeProvider.Setup(d => d.GetCurrentTime()).Returns(today);
    //
    var mockFileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
        {
            { @"Extras/startup.txt", new MockFileData("傑士伯") },
        }
    );


    // Act
    var target = new LottoService(mockRandomGenerator.Object, mockDateTimeProvider.Object, mockFileSystem);
    var actual = target.Lottoing(0, 10);

    // Assert
    expected.ShouldEqual(actual);
}


[TestMethod()]
public void Test_Lottoing_今天是20240105_主辦人宣告開始_輸入亂數範圍_0_10_預期回傳_1_再接再厲()
{
    // Arrange
    var expected = new LottoViewModel()
    { Sponsor="傑士伯", YourNumber = 1, Message = "再接再厲" }
                .ToExpectedObject();

    int fixedValue = 1;
    DateTime today = new(2024, 01, 05);
    var mockRandomGenerator = new Mock<IRandomGenerator>();
    var mockDateTimeProvider = new Mock<IDateTimeProvider>();
    mockRandomGenerator.Setup(r => r.Next(It.IsAny<int>(), It.IsAny<int>())).Returns(fixedValue);
    mockDateTimeProvider.Setup(d => d.GetCurrentTime()).Returns(today);
    var mockFileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
        {
            { @"Extras/startup.txt", new MockFileData("傑士伯") },
        }
    );

    // Act
    var target = new LottoService(mockRandomGenerator.Object, mockDateTimeProvider.Object, mockFileSystem);
    var actual = target.Lottoing(0, 10);

    // Assert
    expected.ShouldEqual(actual);
}


[TestMethod()]
public void Test_Lottoing_今天是20240122_不論主辦人是否宣告開始_輸入亂數範圍_0_10_預期回傳_負1_非每個月5日_不開獎()
{
    // Arrange
    var expected = new LottoViewModel()
    { Sponsor = "", YourNumber = -1, Message = "非每個月5日, 不開獎" }
                .ToExpectedObject();

    int fixedValue = 9;
    DateTime today = new(2024, 01, 22);
    var mockRandomGenerator = new Mock<IRandomGenerator>();
    var mockDateTimeProvider = new Mock<IDateTimeProvider>();
    mockRandomGenerator.Setup(r => r.Next(It.IsAny<int>(), It.IsAny<int>())).Returns(fixedValue);
    mockDateTimeProvider.Setup(d => d.GetCurrentTime()).Returns(today);
    var mockFileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
        {
            { @"Extras/startup.txt", new MockFileData("傑士伯") },
        }
    );

    // Act
    var target = new LottoService(mockRandomGenerator.Object, mockDateTimeProvider.Object, mockFileSystem);
    var actual = target.Lottoing(0, 10);

    // Assert
    expected.ShouldEqual(actual);
}

步驟_5: 針對有開獎的日期, 但主辦人尚未宣告開始, 建立測試案例

[TestMethod()]
public void Test_Lottoing_今天是20240105_但主辦人常未宣告開始_輸入亂數範圍_0_10_預期回傳_負2_主辦人員尚未按下開始按鈕()
{
    // Arrange
    var expected = new LottoViewModel()
    { Sponsor = "", YourNumber = -2, Message = "主辦人員尚未按下[開始]按鈕" }
                .ToExpectedObject();

    int fixedValue = 1;
    DateTime today = new(2024, 01, 05);
    var mockRandomGenerator = new Mock<IRandomGenerator>();
    var mockDateTimeProvider = new Mock<IDateTimeProvider>();
    mockRandomGenerator.Setup(r => r.Next(It.IsAny<int>(), It.IsAny<int>())).Returns(fixedValue);
    mockDateTimeProvider.Setup(d => d.GetCurrentTime()).Returns(today);
    var mockFileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
        {
            //只要不提供檔案路徑, 就會視為 FileNotFound Exception
            //{ @"startup.txt", new MockFileData("傑士伯") },
        }
    );

    // Act
    var target = new LottoService(mockRandomGenerator.Object, mockDateTimeProvider.Object, mockFileSystem);
    var actual = target.Lottoing(0, 10);

    // Assert
    expected.ShouldEqual(actual);
}

步驟_6: 檢查測試的結果

TestResult

結論

System.IO.File 為 static class, System.IO.File.ReadAllText() 為 static method, 故需以一個 interface 進行打包 (Wrap), 讓外界得以操作物件實體, 及其回傳值.

由於 System.IO 下的 static class 及 static method 為數不少, 若要自行一一 mock 會很辛苦, 故找到了一些現成的 nuget 套件進行協助.

只是, 如同前一篇亂數範例所述的, 也會造成開發人員要習慣使用打包後的介面及類別, 這是比較美中不足的地方.

參考文件

public static class File

4.. (Microsoft Learn) File.ReadAllText Method

public static string ReadAllText (string path);

5.. (Ruyut 鹿遊) C# 使用 System.IO.Abstractions 套件來模擬檔案

傑士伯的IT學習之路

2024年1月22日星期一