FileSystemWatcher

MockFileSystem ships a fully functional FileSystemWatcher replacement. It fires the same events as the real one - and crucially, it fires the OS-specific events that the real watcher fires on Linux, Windows and macOS.

Basic usage

var fileSystem = new MockFileSystem();
fileSystem.Initialize().WithSubdirectory("watched");

using var watcher = fileSystem.FileSystemWatcher.New("watched");
var deleted = new ManualResetEventSlim();

watcher.Deleted += (_, _) => deleted.Set();
watcher.EnableRaisingEvents = true;

fileSystem.Directory.Delete("watched");

await Expect.That(deleted.Wait(TimeSpan.FromSeconds(1))).IsTrue();

Reacting to triggered events from a test

MockFileSystem.Watcher.OnTriggered(...) returns an awaitable callback that fires after every IFileSystemWatcher event. Use it to assert what a watcher saw without subscribing to the event yourself:

MockFileSystem fileSystem = new();
fileSystem.Initialize().WithSubdirectory("watched");

using var watcher = fileSystem.FileSystemWatcher.New("watched");
watcher.EnableRaisingEvents = true;

using var triggered = fileSystem.Watcher.OnTriggered(
    change => { /* inspect ChangeDescription */ });

fileSystem.File.WriteAllText("watched/a.txt", "hi");
ChangeDescription[] events = triggered.Wait(count: 1);

Event tables (per OS)

The watcher fires different events depending on whether the source/target is inside, nested under, deeply nested under, or outside the watched path. The table below lists every combination for both values of IncludeSubdirectories - it is also the contract that the MockFileSystem watcher honours when simulating other operating systems.

Location	Description
_	Entry was created or deleted
Outside	Outside the watching path
Inside	Immediately inside the watching path
Nested	Nested under the watching path
Deep	Deeply nested under the watching path

Each cell is IncludeSubdirectories = false / IncludeSubdirectories = true. When both values match, only one is shown. – means no event is raised.

From → To	Linux	Windows	Mac
_ → Inside	Created	Created	Created
Inside → _	Deleted	Deleted	Deleted
_ → Nested	– / Created	– / Created	– / Created
Nested → _	– / Deleted	– / Deleted	– / Deleted
_ → Deep	– / Created	– / Created	– / Created
Deep → _	– / Deleted	– / Deleted	– / Deleted
Outside → Inside	Created	Created	Created
Inside → Inside	Renamed	Renamed	Renamed
Inside → Outside	Deleted	Deleted	Deleted
Outside → Nested	– / Created	– / Created	– / Created
Nested → Nested	– / Renamed	– / Renamed	– / Renamed
Nested → Outside	– / Deleted	– / Deleted	– / Deleted
Outside → Deep	– / Created	– / Created	– / Created
Deep → Deep	– / Renamed	– / Renamed	– / Renamed
Deep → Outside	– / Deleted	– / Deleted	– / Deleted
Inside → Nested	Deleted / Renamed	Deleted / Deleted+Created	Renamed
Inside → Deep	Deleted / Renamed	Deleted / Deleted+Created	Renamed
Nested → Inside	Created / Renamed	Created / Deleted+Created	Created / Renamed
Deep → Inside	Created / Renamed	Created / Deleted+Created	Created / Renamed
Nested → Deep	– / Renamed	– / Deleted+Created	– / Renamed
Deep → Nested	– / Renamed	– / Deleted+Created	– / Renamed