fix: throw an UnauthorizedAccessException immediately when enumerating a directory without access (#860)

This PR fixes a bug where `UnauthorizedAccessException` was not thrown immediately when attempting to enumerate directories without proper access. The fix moves the access control check from inside the enumeration implementation to before enumeration begins, ensuring the exception is thrown synchronously rather than when the enumeration is actually consumed.

### Key Changes
- Access control validation is now performed immediately when enumeration methods are called
- Refactored enumeration implementation to separate access checking from the actual enumeration logic
- Added comprehensive tests to verify the immediate exception behavior

Author: vbreuss

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

@@ -199,8 +199,14 @@ public IEnumerable<IStorageLocation> EnumerateLocations(
 			throw ExceptionFactory.DirectoryNotFound(location.FullPath);
 		}
 
-		return EnumerateLocationsImpl(location, type, requestParentAccess, searchPattern,
-			enumerationOptions, parentContainer);
+		IDisposable parentAccess = new NoOpDisposable();
+		if (requestParentAccess)
+		{
+			parentAccess = parentContainer.RequestAccess(FileAccess.Read, FileShare.ReadWrite);
+		}
+
+		return EnumerateLocationsImpl(location, type, searchPattern,
+			enumerationOptions, parentAccess);
 	}
 
 	/// <summary>
@@ -210,17 +216,10 @@ public IEnumerable<IStorageLocation> EnumerateLocations(
 	private IEnumerable<IStorageLocation> EnumerateLocationsImpl(
 		IStorageLocation location,
 		FileSystemTypes type,
-		bool requestParentAccess,
 		string searchPattern,
 		EnumerationOptions? enumerationOptions,
-		IStorageContainer parentContainer)
+		IDisposable parentAccess)
 	{
-		IDisposable parentAccess = new NoOpDisposable();
-		if (requestParentAccess)
-		{
-			parentAccess = parentContainer.RequestAccess(FileAccess.Read, FileShare.ReadWrite);
-		}
-
 		using (parentAccess)
 		{
 			enumerationOptions ??= EnumerationOptionsHelper.Compatible;

Tests/Testably.Abstractions.Testing.Tests/FileSystem/DirectoryMockTests.cs

@@ -0,0 +1,69 @@
+using Testably.Abstractions.Testing.FileSystem;
+
+namespace Testably.Abstractions.Testing.Tests.FileSystem;
+
+public class DirectoryMockTests
+{
+	[Fact]
+	public async Task
+		EnumerateDirectories_UnauthorizedParentAccess_ShouldThrowUnauthorizedAccessExceptionImmediately()
+	{
+		Skip.IfNot(Test.RunsOnWindows);
+
+		string path = "foo";
+		MockFileSystem fileSystem = new();
+		IDirectoryInfo sut = fileSystem.Directory.CreateDirectory(path);
+		fileSystem.WithAccessControlStrategy(
+			new DefaultAccessControlStrategy((p, _)
+				=> !p.EndsWith(path, StringComparison.Ordinal)));
+
+		void Act() =>
+			_ = fileSystem.Directory.EnumerateDirectories(path);
+
+		await That(Act).Throws<UnauthorizedAccessException>()
+			.WithMessageContaining($"'{sut.FullName}'").And
+			.WithHResult(-2147024891);
+	}
+
+	[Fact]
+	public async Task
+		EnumerateFiles_UnauthorizedParentAccess_ShouldThrowUnauthorizedAccessExceptionImmediately()
+	{
+		Skip.IfNot(Test.RunsOnWindows);
+
+		string path = "foo";
+		MockFileSystem fileSystem = new();
+		IDirectoryInfo sut = fileSystem.Directory.CreateDirectory(path);
+		fileSystem.WithAccessControlStrategy(
+			new DefaultAccessControlStrategy((p, _)
+				=> !p.EndsWith(path, StringComparison.Ordinal)));
+
+		void Act() =>
+			_ = fileSystem.Directory.EnumerateFiles(path);
+
+		await That(Act).Throws<UnauthorizedAccessException>()
+			.WithMessageContaining($"'{sut.FullName}'").And
+			.WithHResult(-2147024891);
+	}
+
+	[Fact]
+	public async Task
+		EnumerateFileSystemEntries_UnauthorizedParentAccess_ShouldThrowUnauthorizedAccessExceptionImmediately()
+	{
+		Skip.IfNot(Test.RunsOnWindows);
+
+		string path = "foo";
+		MockFileSystem fileSystem = new();
+		IDirectoryInfo sut = fileSystem.Directory.CreateDirectory(path);
+		fileSystem.WithAccessControlStrategy(
+			new DefaultAccessControlStrategy((p, _)
+				=> !p.EndsWith(path, StringComparison.Ordinal)));
+
+		void Act() =>
+			_ = fileSystem.Directory.EnumerateFileSystemEntries(path);
+
+		await That(Act).Throws<UnauthorizedAccessException>()
+			.WithMessageContaining($"'{sut.FullName}'").And
+			.WithHResult(-2147024891);
+	}
+}