Temporary directories

Create files and folders

TemporaryDirectory creates files and folders from paths relative to the temporary folder, and returns their FullPath:

using var directory = TemporaryDirectory.Create();

// The parent folders are created when needed
FullPath settings = directory.CreateTextFile("config/settings.json", "{}");
FullPath empty = directory.CreateEmptyFile("logs/app.log");
FullPath cache = directory.CreateDirectory("cache/images");

Assert.Equal(directory.FullPath / "config" / "settings.json", settings);
Assert.Equal(0, new FileInfo(empty).Length);
Assert.True(Directory.Exists(cache));

// GetFullPath and the / operator only compute a path: nothing is created
FullPath report = directory.GetFullPath("reports/today.txt");
Assert.Equal(directory / "reports" / "today.txt", report);
Assert.False(File.Exists(report));

• A relative path can contain several segments, separated by / or by the separator of the platform. The methods that create a file or a folder create the missing parent folders.
• CreateTextFile and CreateTextFileAsync write the text as File.WriteAllText does, in UTF-8 without a byte order mark.

Asynchronous code can write files and dispose the folder asynchronously:

await using var directory = TemporaryDirectory.Create();

var path = await directory.CreateTextFileAsync("data/notes.txt", "Hello");

Assert.Equal("Hello", await File.ReadAllTextAsync(path));

Paths stay inside the folder

Every method checks that the path resolves inside the temporary folder: a path with .. segments that leave it, or a rooted path, throws an ArgumentException. A path that comes from test data cannot write outside the folder by mistake:

using var directory = TemporaryDirectory.Create();

// A path that resolves outside the directory is rejected
Assert.Throws<ArgumentException>(() => directory.GetFullPath("../outside.txt"));
Assert.Throws<ArgumentException>(() => directory.CreateTextFile("data/../../outside.txt", "content"));

// So is a rooted path
var rootedPath = Path.Combine(Path.GetTempPath(), "outside.txt");
Assert.Throws<ArgumentException>(() => directory / rootedPath);

.. segments that stay inside the folder, such as data/../output.txt, are allowed.

Pass the folder to other APIs

TemporaryDirectory converts implicitly to string, to FullPath and to DirectoryInfo, so you can pass the instance itself where an API expects a folder:

using var directory = TemporaryDirectory.Create();
directory.CreateEmptyFile("a.txt");
directory.CreateEmptyFile("b.txt");

// A TemporaryDirectory converts implicitly to string, FullPath and DirectoryInfo
string[] files = Directory.GetFiles(directory);
FullPath path = directory;
DirectoryInfo info = directory;

Assert.HasCount(2, files);
Assert.Equal(directory.FullPath, path);
Assert.Equal(directory.FullPath.Value, info.FullName);

The FullPath property gives the path explicitly. It stays readable after the instance is disposed, although the folder no longer exists. See FullPath to combine, compare and inspect the paths.

Choose where the folder is created

By default, TemporaryDirectory.Create creates the folder in a MezTD folder of the temporary folder of the user (Path.GetTempPath()). Pass another folder to create it there instead:

// Create the directory in a folder of your choice instead of the shared one
FullPath root = FullPath.GetTempPath() / "MyApp.Tests";
using var directory = TemporaryDirectory.Create(root);

Assert.Equal(root, directory.FullPath.Parent);

• The root folder is created if it does not exist. It is not deleted: only the unique folder created in it is.
• The name of the unique folder is the UTC date and time (yyyyMMdd_HHmmss), an underscore and a GUID.
• On Linux and macOS, only the current user can access the root folder. When it already exists and other users can access it, its permissions are tightened. When it belongs to another user, Create throws an UnauthorizedAccessException: choose a root folder of your own.

Deletion

Disposing the instance (Dispose or DisposeAsync) deletes the folder and everything it contains:

• Read-only files are deleted: their read-only attribute is removed first.
• A file that another process holds open is retried a few times, a short time apart, before the error is reported.
• A symbolic link in the folder is deleted as a link: the file or folder it points to is not deleted.
• Disposing an instance twice does nothing. A folder created again at the same path, after the first disposal, is not deleted.
• After disposal, the methods that create or compute a path throw an ObjectDisposedException.

Windows Explorer

On Windows, OpenInExplorer opens the folder in Windows Explorer, which helps to look at the files while debugging a test.