fix: Align MockDirectory and MockFile behavior with .NET's System.IO classes (#1190)

* fix: Align MockDirectory behavior with System.IO.Directory when deleting files

The MockDirectory class previously did not replicate the behavior of
System.IO.Directory when calling the Delete method on a file path. In
System.IO.Directory, an IOException is thrown if the specified path
points to a file instead of a directory.

This commit updates MockDirectory to ensure it throws an IOException in
this scenario, maintaining consistency with the expected behavior of
System.IO.Directory.

* fix: Align MockFile behavior with System.IO.File when deleting directories

The MockFile class previously did not replicate the behavior of
System.IO.File when calling the Delete method on a directory path. In
System.IO.File, an UnauthorizedAccessException is thrown if the
specified path points to a directory instead of a file.

This commit updates MockFile to ensure it throws an
UnauthorizedAccessException in this scenario, maintaining consistency
with the expected behavior of System.IO.File.

Author: WestRyanK

src/TestableIO.System.IO.Abstractions.TestingHelpers/MockDirectory.cs

@@ -158,6 +158,12 @@ public override void Delete(string path, bool recursive)
                                       " is not an empty directory.");
             }
 
+            bool isFile = !mockFileDataAccessor.GetFile(path).IsDirectory;
+            if (isFile)
+            {
+                throw new IOException("The directory name is invalid.");
+            }
+
             foreach (var affectedPath in affectedPaths)
             {
                 mockFileDataAccessor.RemoveFile(affectedPath);

src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFile.cs

@@ -231,6 +231,11 @@ public override void Delete(string path)
                 throw CommonExceptions.ProcessCannotAccessFileInUse(path);
             }
 
+            if (file != null && file.IsDirectory)
+            {
+                throw new UnauthorizedAccessException($"Access to the path '{path}' is denied.");
+            }
+
             mockFileDataAccessor.RemoveFile(path);
         }
 

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryTests.cs

@@ -1018,6 +1018,22 @@ public void MockDirectory_Delete_ShouldDeleteDirectoryRecursively()
             Assert.That(fileSystem.Directory.Exists(XFS.Path(@"c:\bar\bar2")), Is.False);
         }
 
+        [Test]
+        public void MockDirectory_Delete_ShouldThrowIOException_WhenPathIsAFile()
+        {
+            // Arrange
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"c:\foo.txt"), new MockFileData("Demo text content") },
+            });
+
+            // Act
+            TestDelegate action = () => fileSystem.Directory.Delete(XFS.Path(@"c:\foo.txt"));
+
+            // Assert
+            Assert.Throws<IOException>(action);
+        }
+
         [Test]
         public void MockDirectory_GetFileSystemEntries_Returns_Files_And_Directories()
         {

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileTests.cs

@@ -495,6 +495,22 @@ public void MockFile_Delete_No_File_Does_Nothing()
             fileSystem.File.Delete(filePath);
         }
 
+        [Test]
+        public void MockFile_Delete_ShouldThrowUnauthorizedAccessException_WhenPathIsADirectory()
+        {
+            // Arrange
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"c:\bar"), new MockDirectoryData() },
+            });
+
+            // Act
+            TestDelegate action = () => fileSystem.File.Delete(XFS.Path(@"c:\bar"));
+
+            // Assert
+            Assert.Throws<UnauthorizedAccessException>(action);
+        }
+
         [Test]
         public void MockFile_AppendText_AppendTextToAnExistingFile()
         {