fix: Align MockDirectory and MockFile behavior with .NET's System.IO classes

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 @@
             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()
         {
@@ -2069,7 +2085,7 @@
             var fileSystem = new MockFileSystem();
 
             // Act
             Assert.Throws<DirectoryNotFoundException>(() => fileSystem.Directory.GetAccessControl(XFS.Path(@"c:\foo")));
         }
 
         [Test]

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

@@ -495,6 +495,22 @@
             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()
         {
@@ -585,7 +601,7 @@
             });
 
             // Act
             fileSystem.File.Encrypt(filePath);
             var attributes = fileSystem.File.GetAttributes(filePath);
 
             // Assert
@@ -603,10 +619,10 @@
             {
                 {filePath, fileData }
             });
             fileSystem.File.Encrypt(filePath);
 
             // Act
             fileSystem.File.Decrypt(filePath);
             var attributes = fileSystem.File.GetAttributes(filePath);
 
             // Assert