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Drives

MockFileSystem supports multiple drives with independent quotas. This is most useful when simulating Windows, where drive letters carry meaning, but the main drive can also be configured on non-Windows hosts.

Adding a drive​

var fileSystem = new MockFileSystem();
fileSystem
    .WithDrive("D:", d => d.SetTotalSize(1024 * 1024)) // 1 MiB total
    .InitializeIn("D:")
    .WithFile("foo.txt")
    .WithSubdirectory("sub-dir").Initialized(s => s
        .WithAFile(".json").Which(
            f => f.HasStringContent("{\"count\":1}")));

This adds a D: drive limited to 1 MiB and seeds it with an empty foo.txt and a sub-directory containing one randomly named JSON file.

Limiting the main drive​

WithDrive without an argument configures the default drive (works on any OS):

var fileSystem = new MockFileSystem();
fileSystem.WithDrive(d => d.SetTotalSize(20));

// Throws IOException - not enough space on the disk
fileSystem.File.WriteAllText("foo", "some text longer than 20 bytes");

When a drive runs out of space, every file operation that writes content throws IOException, exactly as on the real system.

AvailableFreeSpace tracks every byte written, appended or freed:

MockFileSystem fileSystem = new MockFileSystem()
    .WithDrive("C:\\", d => d.SetTotalSize(100));
IDriveInfo drive = fileSystem.GetDefaultDrive();

drive.AvailableFreeSpace; // 100

fileSystem.File.WriteAllText("foo.txt", "This is a text with 29 bytes.");
drive.AvailableFreeSpace; // 71

fileSystem.File.AppendAllText("foo.txt", "Another 17 bytes.");
drive.AvailableFreeSpace; // 54

fileSystem.File.WriteAllBytes("bar.bin", new byte[90]); // throws IOException
drive.AvailableFreeSpace; // still 54 - the failed write did not consume space

fileSystem.File.Delete("foo.txt");
drive.AvailableFreeSpace; // back to 100

UNC drives​

WithUncDrive("//server") registers a Universal Naming Convention path so reads and writes against \\server\share\... succeed in the mock:

MockFileSystem fileSystem = new();
fileSystem.WithUncDrive(@"//build-server");

fileSystem.File.WriteAllText(@"//build-server/share/foo.txt", "hi");
IDriveInfo drive = fileSystem.DriveInfo.New(@"//build-server");
drive.IsReady; // true

UNC drives don't appear in DriveInfo.GetDrives() - they're addressable but not enumerated, matching the real behaviour.

Inspecting drives​

fileSystem.DriveInfo.GetDrives() returns the registered drives. The objects are full IDriveInfo instances and report TotalSize, AvailableFreeSpace, DriveFormat, VolumeLabel and so on.

fileSystem.GetDefaultDrive() returns the drive backing the current working directory - convenient when you need to assert against the same drive MockFileSystem is using by default.