Fix DirectoryMock.EnumerateDirectories immediate exception throwing

Split InMemoryStorage.EnumerateLocations into validation and implementation methods.
Validation and exceptions now occur immediately when method is called,
while enumeration logic happens during iteration as expected.

Co-authored-by: vbreuss <3438234+vbreuss@users.noreply.github.com>

Author: Copilot

Source/Testably.Abstractions.Testing/Storage/InMemoryStorage.cs

@@ -193,12 +193,29 @@ public IEnumerable<IStorageLocation> EnumerateLocations(
 		string searchPattern = EnumerationOptionsHelper.DefaultSearchPattern,
 		EnumerationOptions? enumerationOptions = null)
 	{
+		// Perform immediate validation and throw exceptions if necessary
 		ValidateExpression(searchPattern);
 		if (!_containers.TryGetValue(location, out IStorageContainer? parentContainer))
 		{
 			throw ExceptionFactory.DirectoryNotFound(location.FullPath);
 		}
 
+		// Return the actual enumeration implementation
+		return EnumerateLocationsImpl(location, type, requestParentAccess, searchPattern, enumerationOptions, parentContainer);
+	}
+
+	/// <summary>
+	/// Internal implementation of location enumeration that uses yield return.
+	/// This method contains the actual enumeration logic and is only called after validation passes.
+	/// </summary>
+	private IEnumerable<IStorageLocation> EnumerateLocationsImpl(
+		IStorageLocation location,
+		FileSystemTypes type,
+		bool requestParentAccess,
+		string searchPattern,
+		EnumerationOptions? enumerationOptions,
+		IStorageContainer parentContainer)
+	{
 		IDisposable parentAccess = new NoOpDisposable();
 		if (requestParentAccess)
 		{

Tests/Testably.Abstractions.Tests/FileSystem/Directory/EnumerateDirectoriesTests.cs

@@ -41,6 +41,23 @@ await That(Act).Throws<DirectoryNotFoundException>()
 		await That(FileSystem.Directory.Exists(path)).IsFalse();
 	}
 
+	[Theory]
+	[AutoData]
+	public async Task
+		EnumerateDirectories_MissingDirectory_ShouldThrowDirectoryNotFoundExceptionImmediately(
+			string path)
+	{
+		string expectedPath = FileSystem.Path.Combine(BasePath, path);
+
+		void Act() =>
+			_ = FileSystem.Directory.EnumerateDirectories(path);
+
+		await That(Act).Throws<DirectoryNotFoundException>()
+			.WithMessageContaining($"'{expectedPath}'").And
+			.WithHResult(-2147024893);
+		await That(FileSystem.Directory.Exists(path)).IsFalse();
+	}
+
 	[Fact]
 	public async Task EnumerateDirectories_RelativePath_ShouldNotIncludeTrailingSlash()
 	{

Tests/Testably.Abstractions.Tests/FileSystem/Directory/EnumerateFileSystemInfosTests.cs

@@ -28,6 +28,23 @@ await That(Act).Throws<DirectoryNotFoundException>()
 		await That(FileSystem.Directory.Exists(path)).IsFalse();
 	}
 
+	[Theory]
+	[AutoData]
+	public async Task
+		EnumerateFileSystemEntries_MissingDirectory_ShouldThrowDirectoryNotFoundExceptionImmediately(
+			string path)
+	{
+		string expectedPath = FileSystem.Path.Combine(BasePath, path);
+
+		void Act() =>
+			_ = FileSystem.Directory.EnumerateFileSystemEntries(path);
+
+		await That(Act).Throws<DirectoryNotFoundException>()
+			.WithMessageContaining($"'{expectedPath}'").And
+			.WithHResult(-2147024893);
+		await That(FileSystem.Directory.Exists(path)).IsFalse();
+	}
+
 	[Theory]
 	[AutoData]
 	public async Task

Tests/Testably.Abstractions.Tests/FileSystem/Directory/EnumerateFilesTests.cs

@@ -25,6 +25,23 @@ await That(Act).Throws<DirectoryNotFoundException>()
 		await That(FileSystem.Directory.Exists(path)).IsFalse();
 	}
 
+	[Theory]
+	[AutoData]
+	public async Task
+		EnumerateFiles_MissingDirectory_ShouldThrowDirectoryNotFoundExceptionImmediately(
+			string path)
+	{
+		string expectedPath = FileSystem.Path.Combine(BasePath, path);
+
+		void Act() =>
+			_ = FileSystem.Directory.EnumerateFiles(path);
+
+		await That(Act).Throws<DirectoryNotFoundException>()
+			.WithMessageContaining($"'{expectedPath}'").And
+			.WithHResult(-2147024893);
+		await That(FileSystem.Directory.Exists(path)).IsFalse();
+	}
+
 	[Theory]
 	[AutoData]
 	public async Task