Expand WinUI FileSystemAdapter test coverage: functional combinations and full guard coverage

[Copilot]

Tests were limited to a subset of argument-guard checks and shallow existence assertions — no content verification, no collision-option combinations, and many handler overloads were untested entirely.

Argument guard completeness (FileSystemAdapterTests.cs)

Added 18 unit tests covering every previously untested type guard:

• WinUIFileHandler — second-argument guards for CopyAndReplaceAsync, CopyAsync, MoveAndReplaceAsync, and all three MoveAsync overloads
• WinUIFolderHandler — all overloads and methods with no prior guard test: CreateFileAsync(+option), CreateFolderAsync(+option), DeleteAsync(+option), GetFileAsync (all-files), GetFoldersAsync, GetItemAsync, GetItemsAsync, GetParentAsync, RenameAsync(+option), TryGetItemAsync

Destination-guard tests obtain a real WinUIFile via GetFileFromPathAsync (the only way to construct the internal type) so the first guard passes and the second is the code path under test:

[Test]
public async Task WinUIFileHandler_CopyAsync_ThrowsArgumentException_WhenDestFolderNotWinUIFolder()
{
    var handler = FileSystemProvider.Instance.GetRequiredService<IFileHandler>();
    var tempPath = Path.GetTempFileName();
    try
    {
        var realSource = await handler.GetFileFromPathAsync(tempPath); // passes first guard

        var act = async () => await handler.CopyAsync(realSource, Substitute.For<IFolder>(), "file.txt", NameCollisionOption.ReplaceExisting);

        await act.Should().ThrowAsync<ArgumentException>(); // second guard fires
    }
    finally { File.Delete(tempPath); }
}

Functional integration coverage (FileSystemAdapterIntegrationTests.cs)

Added 32 integration tests across 11 new regions verifying actual behaviour and data correctness:

• Content preservation — copy/move/replace carry byte content to destination; source absent after move
• All collision combinations for CopyAsync, MoveAsync, RenameAsync, CreateFileAsync, CreateFolderAsync — FailIfExists throws IOException; GenerateUniqueName leaves both items on disk; ReplaceExisting overwrites content / removes old path
• Return-value precision — Path, Name, FolderRelativeId exact values; GetItemAsync returns IFile vs IFolder correctly; GetSizeAsync returns exactly 5UL for a known 5-byte file
• Empty folder edge cases — GetFileAsync, GetFoldersAsync, GetItemsAsync return empty (not null/error)
• Not-found error — GetItemAsync throws FileNotFoundException
• Rename removes old path — both old-gone and new-present asserted
• OpenAsync(AllowReadersAndWriters) and StorageDeletionOption.Default — previously untested overloads

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• az667904.vo.msecnd.net
  • Triggering command: /usr/share/dotnet/dotnet /usr/share/dotnet/dotnet /usr/share/dotnet/sdk/10.0.102/MSBuild.dll /noautoresponse /nologo /nodemode:1 /nodeReuse:true /low:false (dns block)
• vortex.data.microsoft.com
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If you need me to access, download, or install something from one of these locations, you can either:

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[Copilot]

Just as a heads up, I was blocked by some firewall rules while working on your feedback. Expand below for details.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• az667904.vo.msecnd.net
  • Triggering command: /usr/share/dotnet/dotnet /usr/share/dotnet/dotnet /usr/share/dotnet/sdk/10.0.102/MSBuild.dll /noautoresponse /nologo /nodemode:1 /nodeReuse:true /low:false (dns block)
• vortex.data.microsoft.com
  • Triggering command: /usr/share/dotnet/dotnet /usr/share/dotnet/dotnet /usr/share/dotnet/sdk/10.0.102/MSBuild.dll /noautoresponse /nologo /nodemode:1 /nodeReuse:true /low:false (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)