Testably · vbreuss · Feb 1, 2026 · Feb 1, 2026 · Feb 1, 2026 · Feb 1, 2026
diff --git a/Source/Testably.Abstractions.Testing/FileSystem/ChangeHandler.cs b/Source/Testably.Abstractions.Testing/FileSystem/ChangeHandler.cs
@@ -4,8 +4,8 @@
 
 namespace Testably.Abstractions.Testing.FileSystem;
 
-internal sealed class ChangeHandler : IInterceptionHandler,
-	INotificationHandler
+internal sealed class ChangeHandler
+	: IInterceptionHandler, INotificationHandler, IWatcherTriggeredHandler
 {
 	private readonly Notification.INotificationFactory<ChangeDescription>
 		_changeOccurredCallbacks = Notification.CreateFactory<ChangeDescription>();
@@ -15,6 +15,9 @@ private readonly Notification.INotificationFactory<ChangeDescription>
 
 	private readonly MockFileSystem _mockFileSystem;
 
+	private readonly Notification.INotificationFactory<ChangeDescription>
+		_watcherNotificationTriggeredCallbacks = Notification.CreateFactory<ChangeDescription>();
+
 	public ChangeHandler(MockFileSystem mockFileSystem)
 	{
 		_mockFileSystem = mockFileSystem;
@@ -25,8 +28,7 @@ public ChangeHandler(MockFileSystem mockFileSystem)
 	/// <inheritdoc cref="IFileSystemEntity.FileSystem" />
 	public IFileSystem FileSystem => _mockFileSystem;
 
-	/// <inheritdoc
-	///     cref="IInterceptionHandler.Event" />
+	/// <inheritdoc cref="IInterceptionHandler.Event" />
 	public IAwaitableCallback<ChangeDescription> Event(
 		Action<ChangeDescription> interceptionCallback,
 		Func<ChangeDescription, bool>? predicate = null)
@@ -36,15 +38,24 @@ public IAwaitableCallback<ChangeDescription> Event(
 
 	#region INotificationHandler Members
 
-	/// <inheritdoc
-	///     cref="INotificationHandler.OnEvent" />
+	/// <inheritdoc cref="INotificationHandler.OnEvent" />
 	public IAwaitableCallback<ChangeDescription> OnEvent(
 		Action<ChangeDescription>? notificationCallback = null,
 		Func<ChangeDescription, bool>? predicate = null)
 		=> _changeOccurredCallbacks.RegisterCallback(notificationCallback, predicate);
 
 	#endregion
 
+	#region IWatcherTriggeredHandler Members
+
+	/// <inheritdoc cref="IWatcherTriggeredHandler.OnTriggered" />
+	public IAwaitableCallback<ChangeDescription> OnTriggered(
+		Action<ChangeDescription>? triggerCallback = null,
+		Func<ChangeDescription, bool>? predicate = null)
+		=> _watcherNotificationTriggeredCallbacks.RegisterCallback(triggerCallback, predicate);
+
+	#endregion
+
 	internal void NotifyCompletedChange(ChangeDescription? fileSystemChange)
 	{
 		if (fileSystemChange != null)
@@ -65,4 +76,7 @@ internal ChangeDescription NotifyPendingChange(WatcherChangeTypes changeType,
 		_changeOccurringCallbacks.InvokeCallbacks(fileSystemChange);
 		return fileSystemChange;
 	}
+
+	internal void NotifyWatcherTriggeredChange(ChangeDescription fileSystemChange)
+		=> _watcherNotificationTriggeredCallbacks.InvokeCallbacks(fileSystemChange);
 }
diff --git a/Source/Testably.Abstractions.Testing/FileSystem/FileSystemWatcherMock.cs b/Source/Testably.Abstractions.Testing/FileSystem/FileSystemWatcherMock.cs
@@ -446,6 +446,8 @@ private void NotifyChange(ChangeDescription item)
 			{
 				TriggerRenameNotification(item);
 			}
+
+			_fileSystem.ChangeHandler.NotifyWatcherTriggeredChange(item);
 		}
 	}
 
@@ -664,7 +666,8 @@ private void TriggerMacRenameNotification(ChangeDescription item, RenamedContext
 	{
 		CheckRenamePremise(context);
 
-		if (context.ComesFromInside && TryMakeRenamedEventArgs(item, out RenamedEventArgs? eventArgs))
+		if (context.ComesFromInside &&
+		    TryMakeRenamedEventArgs(item, out RenamedEventArgs? eventArgs))
 		{
 			Renamed?.Invoke(this, eventArgs);
 			return;

diff --git a/Source/Testably.Abstractions.Testing/FileSystem/IWatcherTriggeredHandler.cs b/Source/Testably.Abstractions.Testing/FileSystem/IWatcherTriggeredHandler.cs
@@ -0,0 +1,23 @@
+using System;
+
+namespace Testably.Abstractions.Testing.FileSystem;
+
+/// <summary>
+///     The notification handler for triggered notifications from the <see cref="IFileSystemWatcher" />.
+/// </summary>
+public interface IWatcherTriggeredHandler : IFileSystemEntity
+{
+	/// <summary>
+	///     Callback executed after the <see cref="IFileSystemWatcher" /> notified about a change in the
+	///     <see cref="MockFileSystem" /> matching the <paramref name="predicate" />.
+	/// </summary>
+	/// <param name="triggerCallback">The callback to execute after the notification was triggered.</param>
+	/// <param name="predicate">
+	///     (optional) A predicate used to filter which callbacks should be notified.<br />
+	///     If set to <see langword="null" /> (default value) all callbacks are notified.
+	/// </param>
+	/// <returns>An <see cref="IAwaitableCallback{ChangeDescription}" /> to un-register the callback on dispose.</returns>
+	IAwaitableCallback<ChangeDescription> OnTriggered(
+		Action<ChangeDescription>? triggerCallback = null,
+		Func<ChangeDescription, bool>? predicate = null);
+}
diff --git a/Source/Testably.Abstractions.Testing/MockFileSystem.cs b/Source/Testably.Abstractions.Testing/MockFileSystem.cs
@@ -26,6 +26,11 @@ public sealed class MockFileSystem : IFileSystem
 	/// </summary>
 	public INotificationHandler Notify => ChangeHandler;
 
+	/// <summary>
+	///     Get notified of events after they were triggered by a <see cref="IFileSystemWatcher" />.
+	/// </summary>
+	public IWatcherTriggeredHandler Watcher => ChangeHandler;
+
 	/// <summary>
 	///     The used random system.
 	/// </summary>
@@ -223,7 +228,8 @@ public MockFileSystem WithDrive(string? drive,
 		Action<IStorageDrive>? driveCallback = null)
 	{
 		IStorageDrive driveInfoMock =
-			drive == null || string.Equals(drive, Execute.Path.DirectorySeparatorChar.ToString(), StringComparison.Ordinal)
+			drive == null || string.Equals(drive,
+				Execute.Path.DirectorySeparatorChar.ToString(), StringComparison.Ordinal)
 				? Storage.MainDrive
 				: Storage.GetOrAddDrive(drive);
 		driveCallback?.Invoke(driveInfoMock);

diff --git a/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net10.0.txt b/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net10.0.txt
@@ -47,6 +47,10 @@ namespace Testably.Abstractions.Testing.FileSystem
         bool IsAccessGranted(string fullPath, Testably.Abstractions.Helpers.IFileSystemExtensibility extensibility, System.IO.UnixFileMode mode, System.IO.FileAccess requestedAccess);
         void OnSetUnixFileMode(string fullPath, Testably.Abstractions.Helpers.IFileSystemExtensibility extensibility, System.IO.UnixFileMode mode);
     }
+    public interface IWatcherTriggeredHandler : System.IO.Abstractions.IFileSystemEntity
+    {
+        Testably.Abstractions.Testing.IAwaitableCallback<Testably.Abstractions.Testing.FileSystem.ChangeDescription> OnTriggered(System.Action<Testably.Abstractions.Testing.FileSystem.ChangeDescription>? triggerCallback = null, System.Func<Testably.Abstractions.Testing.FileSystem.ChangeDescription, bool>? predicate = null);
+    }
     public class NullAccessControlStrategy : Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy
     {
         public NullAccessControlStrategy() { }
@@ -124,6 +128,7 @@ namespace Testably.Abstractions.Testing
         public Testably.Abstractions.Testing.SimulationMode SimulationMode { get; }
         public Testably.Abstractions.Testing.Statistics.IFileSystemStatistics Statistics { get; }
         public Testably.Abstractions.ITimeSystem TimeSystem { get; }
+        public Testably.Abstractions.Testing.FileSystem.IWatcherTriggeredHandler Watcher { get; }
         public override string ToString() { }
         public Testably.Abstractions.Testing.MockFileSystem WithAccessControlStrategy(Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy accessControlStrategy) { }
         public Testably.Abstractions.Testing.MockFileSystem WithDrive(string? drive, System.Action<Testably.Abstractions.Testing.Storage.IStorageDrive>? driveCallback = null) { }

diff --git a/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net6.0.txt b/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net6.0.txt
@@ -42,6 +42,10 @@ namespace Testably.Abstractions.Testing.FileSystem
     {
         Testably.Abstractions.Testing.FileSystem.SafeFileHandleMock MapSafeFileHandle(Microsoft.Win32.SafeHandles.SafeFileHandle fileHandle);
     }
+    public interface IWatcherTriggeredHandler : System.IO.Abstractions.IFileSystemEntity
+    {
+        Testably.Abstractions.Testing.IAwaitableCallback<Testably.Abstractions.Testing.FileSystem.ChangeDescription> OnTriggered(System.Action<Testably.Abstractions.Testing.FileSystem.ChangeDescription>? triggerCallback = null, System.Func<Testably.Abstractions.Testing.FileSystem.ChangeDescription, bool>? predicate = null);
+    }
     public class NullAccessControlStrategy : Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy
     {
         public NullAccessControlStrategy() { }
@@ -113,6 +117,7 @@ namespace Testably.Abstractions.Testing
         public Testably.Abstractions.Testing.SimulationMode SimulationMode { get; }
         public Testably.Abstractions.Testing.Statistics.IFileSystemStatistics Statistics { get; }
         public Testably.Abstractions.ITimeSystem TimeSystem { get; }
+        public Testably.Abstractions.Testing.FileSystem.IWatcherTriggeredHandler Watcher { get; }
         public override string ToString() { }
         public Testably.Abstractions.Testing.MockFileSystem WithAccessControlStrategy(Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy accessControlStrategy) { }
         public Testably.Abstractions.Testing.MockFileSystem WithDrive(string? drive, System.Action<Testably.Abstractions.Testing.Storage.IStorageDrive>? driveCallback = null) { }

diff --git a/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net8.0.txt b/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net8.0.txt
@@ -47,6 +47,10 @@ namespace Testably.Abstractions.Testing.FileSystem
         bool IsAccessGranted(string fullPath, Testably.Abstractions.Helpers.IFileSystemExtensibility extensibility, System.IO.UnixFileMode mode, System.IO.FileAccess requestedAccess);
         void OnSetUnixFileMode(string fullPath, Testably.Abstractions.Helpers.IFileSystemExtensibility extensibility, System.IO.UnixFileMode mode);
     }
+    public interface IWatcherTriggeredHandler : System.IO.Abstractions.IFileSystemEntity
+    {
+        Testably.Abstractions.Testing.IAwaitableCallback<Testably.Abstractions.Testing.FileSystem.ChangeDescription> OnTriggered(System.Action<Testably.Abstractions.Testing.FileSystem.ChangeDescription>? triggerCallback = null, System.Func<Testably.Abstractions.Testing.FileSystem.ChangeDescription, bool>? predicate = null);
+    }
     public class NullAccessControlStrategy : Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy
     {
         public NullAccessControlStrategy() { }
@@ -124,6 +128,7 @@ namespace Testably.Abstractions.Testing
         public Testably.Abstractions.Testing.SimulationMode SimulationMode { get; }
         public Testably.Abstractions.Testing.Statistics.IFileSystemStatistics Statistics { get; }
         public Testably.Abstractions.ITimeSystem TimeSystem { get; }
+        public Testably.Abstractions.Testing.FileSystem.IWatcherTriggeredHandler Watcher { get; }
         public override string ToString() { }
         public Testably.Abstractions.Testing.MockFileSystem WithAccessControlStrategy(Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy accessControlStrategy) { }
         public Testably.Abstractions.Testing.MockFileSystem WithDrive(string? drive, System.Action<Testably.Abstractions.Testing.Storage.IStorageDrive>? driveCallback = null) { }

diff --git a/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net9.0.txt b/Tests/Api/Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_net9.0.txt
@@ -47,6 +47,10 @@ namespace Testably.Abstractions.Testing.FileSystem
         bool IsAccessGranted(string fullPath, Testably.Abstractions.Helpers.IFileSystemExtensibility extensibility, System.IO.UnixFileMode mode, System.IO.FileAccess requestedAccess);
         void OnSetUnixFileMode(string fullPath, Testably.Abstractions.Helpers.IFileSystemExtensibility extensibility, System.IO.UnixFileMode mode);
     }
+    public interface IWatcherTriggeredHandler : System.IO.Abstractions.IFileSystemEntity
+    {
+        Testably.Abstractions.Testing.IAwaitableCallback<Testably.Abstractions.Testing.FileSystem.ChangeDescription> OnTriggered(System.Action<Testably.Abstractions.Testing.FileSystem.ChangeDescription>? triggerCallback = null, System.Func<Testably.Abstractions.Testing.FileSystem.ChangeDescription, bool>? predicate = null);
+    }
     public class NullAccessControlStrategy : Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy
     {
         public NullAccessControlStrategy() { }
@@ -124,6 +128,7 @@ namespace Testably.Abstractions.Testing
         public Testably.Abstractions.Testing.SimulationMode SimulationMode { get; }
         public Testably.Abstractions.Testing.Statistics.IFileSystemStatistics Statistics { get; }
         public Testably.Abstractions.ITimeSystem TimeSystem { get; }
+        public Testably.Abstractions.Testing.FileSystem.IWatcherTriggeredHandler Watcher { get; }
         public override string ToString() { }
         public Testably.Abstractions.Testing.MockFileSystem WithAccessControlStrategy(Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy accessControlStrategy) { }
         public Testably.Abstractions.Testing.MockFileSystem WithDrive(string? drive, System.Action<Testably.Abstractions.Testing.Storage.IStorageDrive>? driveCallback = null) { }

diff --git a/...Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_netstandard2.0.txt b/...Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_netstandard2.0.txt
@@ -41,6 +41,10 @@ namespace Testably.Abstractions.Testing.FileSystem
     {
         Testably.Abstractions.Testing.FileSystem.SafeFileHandleMock MapSafeFileHandle(Microsoft.Win32.SafeHandles.SafeFileHandle fileHandle);
     }
+    public interface IWatcherTriggeredHandler : System.IO.Abstractions.IFileSystemEntity
+    {
+        Testably.Abstractions.Testing.IAwaitableCallback<Testably.Abstractions.Testing.FileSystem.ChangeDescription> OnTriggered(System.Action<Testably.Abstractions.Testing.FileSystem.ChangeDescription>? triggerCallback = null, System.Func<Testably.Abstractions.Testing.FileSystem.ChangeDescription, bool>? predicate = null);
+    }
     public class NullAccessControlStrategy : Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy
     {
         public NullAccessControlStrategy() { }
@@ -111,6 +115,7 @@ namespace Testably.Abstractions.Testing
         public Testably.Abstractions.Testing.SimulationMode SimulationMode { get; }
         public Testably.Abstractions.Testing.Statistics.IFileSystemStatistics Statistics { get; }
         public Testably.Abstractions.ITimeSystem TimeSystem { get; }
+        public Testably.Abstractions.Testing.FileSystem.IWatcherTriggeredHandler Watcher { get; }
         public override string ToString() { }
         public Testably.Abstractions.Testing.MockFileSystem WithAccessControlStrategy(Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy accessControlStrategy) { }
         public Testably.Abstractions.Testing.MockFileSystem WithDrive(string? drive, System.Action<Testably.Abstractions.Testing.Storage.IStorageDrive>? driveCallback = null) { }

diff --git a/...Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_netstandard2.1.txt b/...Testably.Abstractions.Api.Tests/Expected/Testably.Abstractions.Testing_netstandard2.1.txt
@@ -41,6 +41,10 @@ namespace Testably.Abstractions.Testing.FileSystem
     {
         Testably.Abstractions.Testing.FileSystem.SafeFileHandleMock MapSafeFileHandle(Microsoft.Win32.SafeHandles.SafeFileHandle fileHandle);
     }
+    public interface IWatcherTriggeredHandler : System.IO.Abstractions.IFileSystemEntity
+    {
+        Testably.Abstractions.Testing.IAwaitableCallback<Testably.Abstractions.Testing.FileSystem.ChangeDescription> OnTriggered(System.Action<Testably.Abstractions.Testing.FileSystem.ChangeDescription>? triggerCallback = null, System.Func<Testably.Abstractions.Testing.FileSystem.ChangeDescription, bool>? predicate = null);
+    }
     public class NullAccessControlStrategy : Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy
     {
         public NullAccessControlStrategy() { }
@@ -111,6 +115,7 @@ namespace Testably.Abstractions.Testing
         public Testably.Abstractions.Testing.SimulationMode SimulationMode { get; }
         public Testably.Abstractions.Testing.Statistics.IFileSystemStatistics Statistics { get; }
         public Testably.Abstractions.ITimeSystem TimeSystem { get; }
+        public Testably.Abstractions.Testing.FileSystem.IWatcherTriggeredHandler Watcher { get; }
         public override string ToString() { }
         public Testably.Abstractions.Testing.MockFileSystem WithAccessControlStrategy(Testably.Abstractions.Testing.FileSystem.IAccessControlStrategy accessControlStrategy) { }
         public Testably.Abstractions.Testing.MockFileSystem WithDrive(string? drive, System.Action<Testably.Abstractions.Testing.Storage.IStorageDrive>? driveCallback = null) { }

diff --git a/Tests/Testably.Abstractions.Testing.Tests/FileSystem/ChangeHandlerTests.cs b/Tests/Testably.Abstractions.Testing.Tests/FileSystem/ChangeHandlerTests.cs
@@ -1,5 +1,6 @@
 using aweXpect.Synchronous;
 using System.IO;
+using Testably.Abstractions.Testing.FileSystem;
 
 namespace Testably.Abstractions.Testing.Tests.FileSystem;
 
@@ -98,6 +99,39 @@ public async Task ExecuteCallback_ShouldTriggerNotification(
 		await That(receivedPath).IsEqualTo(FileSystem.Path.GetFullPath(path));
 	}
 
+	[Fact]
+	public async Task Watcher_ShouldNotTriggerWhenFileSystemWatcherDoesNotMatch()
+	{
+		FileSystem.Directory.CreateDirectory("bar");
+		IFileSystemWatcher watcher = FileSystem.FileSystemWatcher.New("bar");
+		watcher.EnableRaisingEvents = true;
+
+		IAwaitableCallback<ChangeDescription> onEvent = FileSystem.Watcher.OnTriggered();
+
+		void Act() =>
+			onEvent.Wait(timeout: 100,
+				executeWhenWaiting: () => FileSystem.File.WriteAllText(@"foo.txt", "some-text"));
+
+		await That(Act).Throws<TimeoutException>();
+	}
+
+	[Fact]
+	public async Task Watcher_ShouldTriggerWhenFileSystemWatcherSendsNotification()
+	{
+		bool isTriggered = false;
+		FileSystem.InitializeIn(".");
+		IFileSystemWatcher watcher = FileSystem.FileSystemWatcher.New(".");
+		watcher.Created += (_, _) => isTriggered = true;
+		watcher.EnableRaisingEvents = true;
+
+		IAwaitableCallback<ChangeDescription> onEvent = FileSystem.Watcher.OnTriggered();
+
+		onEvent.Wait(timeout: 5000,
+			executeWhenWaiting: () => FileSystem.File.WriteAllText(@"foo.txt", "some-text"));
+
+		await That(isTriggered).IsTrue();
+	}
+
 	#region Helpers
 
 	public static