[cmdpal] Migrate some plugin's unit tests from PT run to cmdpal. (#40462)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
Migrate blow plugin's from UT to cmdpal:
1. TimeDate
2. WindowWalker
3. System
4. Registry

This PR is mostly helped by Copilot. Please feel free to change cases in
the future.

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## PR Checklist

- [x] **Closes:** #40461
- [x] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [x] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
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---------

Co-authored-by: Yu Leng <yuleng@microsoft.com>

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.WindowWalker.UnitTests/Microsoft.CmdPal.Ext.WindowWalker.UnitTests.csproj

@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <!-- Look at Directory.Build.props in root for common stuff as well -->
+  <Import Project="..\..\..\..\Common.Dotnet.CsWinRT.props" />
+
+  <PropertyGroup>
+    <IsPackable>false</IsPackable>
+    <IsTestProject>true</IsTestProject>
+    <RootNamespace>Microsoft.CmdPal.Ext.WindowWalker.UnitTests</RootNamespace>
+    <OutputPath>$(SolutionDir)$(Platform)\$(Configuration)\WinUI3Apps\CmdPal\tests\</OutputPath>
+    <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
+    <AppendRuntimeIdentifierToOutputPath>false</AppendRuntimeIdentifierToOutputPath>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Moq" />
+    <PackageReference Include="MSTest" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\..\..\common\ManagedCommon\ManagedCommon.csproj" />
+    <ProjectReference Include="..\..\ext\Microsoft.CmdPal.Ext.WindowWalker\Microsoft.CmdPal.Ext.WindowWalker.csproj" />
+    <ProjectReference Include="..\..\extensionsdk\Microsoft.CommandPalette.Extensions.Toolkit\Microsoft.CommandPalette.Extensions.Toolkit.csproj" />
+  </ItemGroup>
+</Project>

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.WindowWalker.UnitTests/PluginSettingsTests.cs

@@ -0,0 +1,60 @@
+// 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;
+using System.Reflection;
+
+using Microsoft.CmdPal.Ext.WindowWalker.Helpers;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Microsoft.CmdPal.Ext.WindowWalker.UnitTests;
+
+[TestClass]
+public class PluginSettingsTests
+{
+    [DataTestMethod]
+    [DataRow("ResultsFromVisibleDesktopOnly")]
+    [DataRow("SubtitleShowPid")]
+    [DataRow("SubtitleShowDesktopName")]
+    [DataRow("ConfirmKillProcess")]
+    [DataRow("KillProcessTree")]
+    [DataRow("OpenAfterKillAndClose")]
+    [DataRow("HideKillProcessOnElevatedProcesses")]
+    [DataRow("HideExplorerSettingInfo")]
+    [DataRow("InMruOrder")]
+    public void DoesSettingExist(string name)
+    {
+        // Setup
+        Type settings = SettingsManager.Instance?.GetType();
+
+        // Act
+        var result = settings?.GetProperty(name, BindingFlags.Public | BindingFlags.Instance);
+
+        // Assert
+        Assert.IsNotNull(result);
+    }
+
+    [DataTestMethod]
+    [DataRow("ResultsFromVisibleDesktopOnly", false)]
+    [DataRow("SubtitleShowPid", false)]
+    [DataRow("SubtitleShowDesktopName", true)]
+    [DataRow("ConfirmKillProcess", true)]
+    [DataRow("KillProcessTree", false)]
+    [DataRow("OpenAfterKillAndClose", false)]
+    [DataRow("HideKillProcessOnElevatedProcesses", false)]
+    [DataRow("HideExplorerSettingInfo", true)]
+    [DataRow("InMruOrder", true)]
+    public void DefaultValues(string name, bool valueExpected)
+    {
+        // Setup
+        SettingsManager setting = SettingsManager.Instance;
+
+        // Act
+        PropertyInfo propertyInfo = setting?.GetType()?.GetProperty(name, BindingFlags.Public | BindingFlags.Instance);
+        var result = propertyInfo?.GetValue(setting);
+
+        // Assert
+        Assert.AreEqual(valueExpected, result);
+    }
+}