如何使用 System.IO.Abstractions 中的 FileSystemWatcher 来监视模拟文件系统？

Question

我正在尝试创建一个类来监控 Linux 上的 USB 设备到达和移除。在 Linux 上，USB 设备表示为/dev/bus/usb 下的设备文件，这些设备文件是为响应这些事件而创建/删除的。

似乎跟踪这些事件的最佳方法是使用FileSystemWatcher。为了使类可测试，我使用System.IO.Abstractions 并在构造过程中将IFileSystem 的实例注入到类中。我想要的是创建一些行为类似于FileSystemWatcher 但监视注入的IFileSystem 的更改，而不是直接监视真正的文件系统。

查看System.IO.Abstractions 中的FileSystemWatcherBase 和FileSystemWatcherWrapper，我不知道该怎么做。目前我有这个（我知道这是错误的）：

public DevMonitor(
    [NotNull] IFileSystem fileSystem,
    [NotNull] IDeviceFileParser deviceFileParser,
    [NotNull] ILogger logger,
    [NotNull] string devDirectoryPath = DefaultDevDirectoryPath)
{
    Raise.ArgumentNullException.IfIsNull(logger, nameof(logger));
    Raise.ArgumentNullException.IfIsNull(devDirectoryPath, nameof(devDirectoryPath));

    _fileSystem = fileSystem ?? throw new ArgumentNullException(nameof(fileSystem));
    _deviceFileParser = deviceFileParser ?? throw new ArgumentNullException(nameof(deviceFileParser));
    _logger = logger.ForContext<DevMonitor>();
    _watcher = new FileSystemWatcherWrapper(devDirectoryPath);
}

Answer 1

鉴于System.IO.Abstractions 似乎还不支持这一点，我选择了这个：

我定义了一个扩展IFileSystem 的IWatchableFileSystem 接口：

/// <summary>
/// Represents a(n) <see cref="IFileSystem" /> that can be watched for changes.
/// </summary>
public interface IWatchableFileSystem : IFileSystem
{
    /// <summary>
    /// Creates a <c>FileSystemWatcher</c> that can be used to monitor changes to this file system.
    /// </summary>
    /// <returns>A <c>FileSystemWatcher</c>.</returns>
    FileSystemWatcherBase CreateWatcher();
}

出于生产目的，我将其实现为WatchableFileSystem：

/// <inheritdoc />
public sealed class WatchableFileSystem : IWatchableFileSystem
{
    private readonly IFileSystem _fileSystem;

    /// <summary>
    /// Initializes a new instance of the <see cref="WatchableFileSystem" /> class.
    /// </summary>
    public WatchableFileSystem() => _fileSystem = new FileSystem();

    /// <inheritdoc />
    public DirectoryBase Directory => _fileSystem.Directory;

    /// <inheritdoc />
    public IDirectoryInfoFactory DirectoryInfo => _fileSystem.DirectoryInfo;

    /// <inheritdoc />
    public IDriveInfoFactory DriveInfo => _fileSystem.DriveInfo;

    /// <inheritdoc />
    public FileBase File => _fileSystem.File;

    /// <inheritdoc />
    public IFileInfoFactory FileInfo => _fileSystem.FileInfo;

    /// <inheritdoc />
    public PathBase Path => _fileSystem.Path;

    /// <inheritdoc />
    public FileSystemWatcherBase CreateWatcher() => new FileSystemWatcher();
}

在我的单元测试类中，我将它实现为MockWatchableFileSystem，它将MockFileSystem 和Mock<FileSystemWatcherBase> 公开为我可以用于在我的测试中安排和断言的属性：

private class MockWatchableFileSystem : IWatchableFileSystem
{
    /// <inheritdoc />
    public MockWatchableFileSystem()
    {
        Watcher = new Mock<FileSystemWatcherBase>();
        AsMock = new MockFileSystem();

        AsMock.AddDirectory("/dev/bus/usb");
        Watcher.SetupAllProperties();
    }

    public MockFileSystem AsMock { get; }

    /// <inheritdoc />
    public DirectoryBase Directory => AsMock.Directory;

    /// <inheritdoc />
    public IDirectoryInfoFactory DirectoryInfo => AsMock.DirectoryInfo;

    /// <inheritdoc />
    public IDriveInfoFactory DriveInfo => AsMock.DriveInfo;

    /// <inheritdoc />
    public FileBase File => AsMock.File;

    /// <inheritdoc />
    public IFileInfoFactory FileInfo => AsMock.FileInfo;

    /// <inheritdoc />
    public PathBase Path => AsMock.Path;

    public Mock<FileSystemWatcherBase> Watcher { get; }

    /// <inheritdoc />
    public FileSystemWatcherBase CreateWatcher() => Watcher.Object;
}

最后，在我的客户端类中我可以这样做：

public DevMonitor(
    [NotNull] IWatchableFileSystem fileSystem,
    [NotNull] IDeviceFileParser deviceFileParser,
    [NotNull] ILogger logger,
    [NotNull] string devDirectoryPath = DefaultDevDirectoryPath)
{
    // ...
    _watcher = fileSystem.CreateWatcher();

    _watcher.IncludeSubdirectories = true;
    _watcher.EnableRaisingEvents = true;
    _watcher.Path = devDirectoryPath;
}

在测试期间，客户端获得一个 IWatchableFileSystem 包装 MockFileSystem 并返回一个模拟实例 FileSystemWatcherBase。在生产过程中，它会得到一个 IWatchableFileSystem 包装 FileSystem 并生成 FileSystemWatcher 的唯一实例。