fix(paste): address PR review comments

- Add null check for ParentNode in RemoveUnwantedElements to prevent potential NullReferenceException when wrapper is document root
- Remove unused HtmlAgilityPack import from test file

src/modules/AdvancedPaste/AdvancedPaste.UnitTests/HelpersTests/MarkdownHelperTests.cs

@@ -0,0 +1,167 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Reflection;
+using AdvancedPaste.Helpers;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace AdvancedPaste.UnitTests.HelpersTests;
+
+[TestClass]
+public sealed class MarkdownHelperTests
+{
+    /// <summary>
+    /// Helper method to invoke the private CleanHtml method for testing.
+    /// </summary>
+    private static string InvokeCleanHtml(string html)
+    {
+        var methodInfo = typeof(MarkdownHelper).GetMethod("CleanHtml", BindingFlags.NonPublic | BindingFlags.Static);
+        return (string)methodInfo!.Invoke(null, [html])!;
+    }
+
+    /// <summary>
+    /// Helper method to invoke the private ConvertHtmlToMarkdown method for testing.
+    /// </summary>
+    private static string InvokeConvertHtmlToMarkdown(string html)
+    {
+        var methodInfo = typeof(MarkdownHelper).GetMethod("ConvertHtmlToMarkdown", BindingFlags.NonPublic | BindingFlags.Static);
+        return (string)methodInfo!.Invoke(null, [html])!;
+    }
+
+    [TestMethod]
+    public void CleanHtml_GoogleSheetsWrapper_RemovesWrapperPreservesTable()
+    {
+        // Arrange - Google Sheets HTML with wrapper element
+        const string googleSheetsHtml = @"<google-sheets-html-origin>
+<style type=""text/css""><!--td {border: 1px solid #cccccc;}--></style>
+<table xmlns=""http://www.w3.org/1999/xhtml"" cellspacing=""0"" cellpadding=""0"" dir=""ltr"" border=""1"" data-sheets-root=""1"">
+<colgroup><col width=""100""><col width=""100""></colgroup>
+<tbody><tr><td>A</td><td>B</td></tr><tr><td>1</td><td>2</td></tr></tbody>
+</table>
+</google-sheets-html-origin>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(googleSheetsHtml);
+
+        // Assert - wrapper and style should be removed, table preserved
+        Assert.IsFalse(cleanedHtml.Contains("google-sheets-html-origin"), "Google Sheets wrapper should be removed");
+        Assert.IsFalse(cleanedHtml.Contains("<style"), "Style element should be removed");
+        Assert.IsFalse(cleanedHtml.Contains("<colgroup"), "Colgroup element should be removed");
+        Assert.IsTrue(cleanedHtml.Contains("<table"), "Table element should be preserved");
+        Assert.IsTrue(cleanedHtml.Contains("<td>A</td>"), "Table content should be preserved");
+    }
+
+    [TestMethod]
+    public void CleanHtml_GoogleSheetsHtml_ConvertsToMarkdownTable()
+    {
+        // Arrange - Google Sheets HTML with wrapper element
+        const string googleSheetsHtml = @"<google-sheets-html-origin>
+<style type=""text/css""><!--td {border: 1px solid #cccccc;}--></style>
+<table xmlns=""http://www.w3.org/1999/xhtml"" cellspacing=""0"" cellpadding=""0"" dir=""ltr"" border=""1"" data-sheets-root=""1"">
+<colgroup><col width=""100""><col width=""100""></colgroup>
+<tbody><tr><td>A</td><td>B</td></tr><tr><td>1</td><td>2</td></tr></tbody>
+</table>
+</google-sheets-html-origin>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(googleSheetsHtml);
+        string markdown = InvokeConvertHtmlToMarkdown(cleanedHtml);
+
+        // Assert - should produce valid Markdown table
+        Assert.IsTrue(markdown.Contains("|"), "Markdown should contain table pipes");
+        Assert.IsTrue(markdown.Contains("A") && markdown.Contains("B"), "Markdown should contain table content");
+        Assert.IsTrue(markdown.Contains("1") && markdown.Contains("2"), "Markdown should contain table data");
+        Assert.IsFalse(markdown.Contains("<google-sheets-html-origin>"), "Markdown should not contain HTML wrapper");
+    }
+
+    [TestMethod]
+    public void CleanHtml_ExcelHtml_ConvertsToMarkdownTable()
+    {
+        // Arrange - Typical Excel HTML (for regression testing)
+        const string excelHtml = @"<table border=""0"" cellpadding=""0"" cellspacing=""0"" width=""192"">
+<tbody><tr height=""20""><td height=""20"" width=""64"">Name</td><td width=""64"">Value</td><td width=""64"">Status</td></tr>
+<tr height=""20""><td height=""20"">Item1</td><td>100</td><td>Active</td></tr>
+<tr height=""20""><td height=""20"">Item2</td><td>200</td><td>Inactive</td></tr>
+</tbody></table>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(excelHtml);
+        string markdown = InvokeConvertHtmlToMarkdown(cleanedHtml);
+
+        // Assert - Excel HTML should still convert correctly
+        Assert.IsTrue(markdown.Contains("|"), "Markdown should contain table pipes");
+        Assert.IsTrue(markdown.Contains("Name"), "Markdown should contain header content");
+        Assert.IsTrue(markdown.Contains("Item1") && markdown.Contains("Item2"), "Markdown should contain row data");
+    }
+
+    [TestMethod]
+    public void CleanHtml_StyleElement_IsRemoved()
+    {
+        // Arrange
+        const string htmlWithStyle = @"<html><head><style>body { color: red; }</style></head><body><p>Text</p></body></html>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(htmlWithStyle);
+
+        // Assert
+        Assert.IsFalse(cleanedHtml.Contains("<style"), "Style element should be removed");
+        Assert.IsTrue(cleanedHtml.Contains("<p>Text</p>") || cleanedHtml.Contains("Text"), "Content should be preserved");
+    }
+
+    [TestMethod]
+    public void CleanHtml_ColgroupElement_IsRemoved()
+    {
+        // Arrange
+        const string htmlWithColgroup = @"<table><colgroup><col width=""100""></colgroup><tbody><tr><td>Data</td></tr></tbody></table>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(htmlWithColgroup);
+
+        // Assert
+        Assert.IsFalse(cleanedHtml.Contains("<colgroup"), "Colgroup element should be removed");
+        Assert.IsTrue(cleanedHtml.Contains("<table"), "Table element should be preserved");
+        Assert.IsTrue(cleanedHtml.Contains("Data"), "Table content should be preserved");
+    }
+
+    [TestMethod]
+    public void CleanHtml_ScriptElement_IsRemoved()
+    {
+        // Arrange
+        const string htmlWithScript = @"<html><body><script>alert('test');</script><p>Content</p></body></html>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(htmlWithScript);
+
+        // Assert
+        Assert.IsFalse(cleanedHtml.Contains("<script"), "Script element should be removed");
+        Assert.IsTrue(cleanedHtml.Contains("Content"), "Content should be preserved");
+    }
+
+    [TestMethod]
+    public void CleanHtml_NestedGoogleSheetsTable_PreservesNestedContent()
+    {
+        // Arrange - More complex Google Sheets HTML
+        const string complexGoogleSheetsHtml = @"<google-sheets-html-origin>
+<style type=""text/css"">td {border: 1px solid #ccc;}</style>
+<table data-sheets-root=""1"">
+<colgroup><col width=""100""><col width=""150""><col width=""100""></colgroup>
+<tbody>
+<tr><td>Header1</td><td>Header2</td><td>Header3</td></tr>
+<tr><td>Row1Col1</td><td>Row1Col2</td><td>Row1Col3</td></tr>
+<tr><td>Row2Col1</td><td>Row2Col2</td><td>Row2Col3</td></tr>
+</tbody>
+</table>
+</google-sheets-html-origin>";
+
+        // Act
+        string cleanedHtml = InvokeCleanHtml(complexGoogleSheetsHtml);
+        string markdown = InvokeConvertHtmlToMarkdown(cleanedHtml);
+
+        // Assert
+        Assert.IsFalse(markdown.Contains("<google-sheets-html-origin>"), "Wrapper should be removed from markdown");
+        Assert.IsTrue(markdown.Contains("Header1"), "Headers should be preserved");
+        Assert.IsTrue(markdown.Contains("Row1Col1"), "Row data should be preserved");
+        Assert.IsTrue(markdown.Contains("Row2Col3"), "All cells should be preserved");
+    }
+}

src/modules/AdvancedPaste/AdvancedPaste/Helpers/MarkdownHelper.cs

@@ -57,6 +57,23 @@ namespace AdvancedPaste.Helpers
         {
             Logger.LogTrace();
 
+            // Unwrap Google Sheets wrapper element (preserve children, remove wrapper)
+            foreach (var googleSheetsWrapper in node.DescendantsAndSelf("google-sheets-html-origin").ToArray())
+            {
+                var parent = googleSheetsWrapper.ParentNode;
+                if (parent == null)
+                {
+                    continue;
+                }
+
+                foreach (var child in googleSheetsWrapper.ChildNodes.ToArray())
+                {
+                    parent.InsertBefore(child, googleSheetsWrapper);
+                }
+
+                googleSheetsWrapper.Remove();
+            }
+
             // Remove specific elements by tag name, CSS class, or other attributes
             // Example: Remove all <script> elements
             foreach (var scriptNode in node.DescendantsAndSelf("script").ToArray())
@@ -64,6 +81,18 @@ namespace AdvancedPaste.Helpers
                 scriptNode.Remove();
             }
 
+            // Remove style elements (CSS not relevant for Markdown)
+            foreach (var styleNode in node.DescendantsAndSelf("style").ToArray())
+            {
+                styleNode.Remove();
+            }
+
+            // Remove colgroup elements (column width info not needed for Markdown)
+            foreach (var colgroupNode in node.DescendantsAndSelf("colgroup").ToArray())
+            {
+                colgroupNode.Remove();
+            }
+
             // Ignore specific elements like <sup> elements
             foreach (var ignoredElement in node.DescendantsAndSelf("sup").ToArray())
             {