[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)?
-->
## 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 -->
## Validation Steps Performed

---------

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

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.Registry/Microsoft.CmdPal.Ext.Registry.csproj

@@ -10,6 +10,13 @@
     <!-- MRT from windows app sdk will search for a pri file with the same name of the module before defaulting to resources.pri -->
     <ProjectPriFileName>Microsoft.CmdPal.Ext.Registry.pri</ProjectPriFileName>
   </PropertyGroup>
+
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+      <_Parameter1>Microsoft.CmdPal.Ext.Registry.UnitTests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
   <ItemGroup>
     <PackageReference Include="System.ServiceProcess.ServiceController" />
   </ItemGroup>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.System/Microsoft.CmdPal.Ext.System.csproj

@@ -33,4 +33,9 @@
       <CustomToolNamespace>Microsoft.CmdPal.Ext.System</CustomToolNamespace>
     </EmbeddedResource>
   </ItemGroup>
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+      <_Parameter1>Microsoft.CmdPal.Ext.System.UnitTests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
 </Project>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.TimeDate/FallbackTimeDateItem.cs

@@ -17,13 +17,16 @@ internal sealed partial class FallbackTimeDateItem : FallbackCommandItem
 {
     private readonly HashSet<string> _validOptions;
     private SettingsManager _settingsManager;
+    private DateTime? _timestamp;
 
-    public FallbackTimeDateItem(SettingsManager settings)
+    public FallbackTimeDateItem(SettingsManager settings, DateTime? timestamp = null)
          : base(new NoOpCommand(), Resources.Microsoft_plugin_timedate_fallback_display_title)
     {
         Title = string.Empty;
         Subtitle = string.Empty;
         _settingsManager = settings;
+        _timestamp = timestamp;
+
         _validOptions = new(StringComparer.OrdinalIgnoreCase)
         {
             Resources.ResourceManager.GetString("Microsoft_plugin_timedate_SearchTagDate", CultureInfo.CurrentCulture),
@@ -49,7 +52,7 @@ internal sealed partial class FallbackTimeDateItem : FallbackCommandItem
             return;
         }
 
-        var availableResults = AvailableResultsList.GetList(false, _settingsManager);
+        var availableResults = AvailableResultsList.GetList(false, _settingsManager, timestamp: _timestamp);
         ListItem result = null;
         var maxScore = 0;
 

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.TimeDate/Helpers/TimeAndDateHelper.cs

@@ -298,6 +298,7 @@ internal static class TimeAndDateHelper
         }
         else
         {
+            inputParsingErrorMsg = Resources.Microsoft_plugin_timedate_InvalidInput_ErrorMessageTitle;
             timestamp = new DateTime(1, 1, 1, 1, 1, 1);
             Logger.LogWarning($"Failed to parse input: '{input}'. Format not recognized.");
             return false;

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.TimeDate/Microsoft.CmdPal.Ext.TimeDate.csproj

@@ -11,6 +11,12 @@
     <ProjectPriFileName>Microsoft.CmdPal.Ext.TimeDate.pri</ProjectPriFileName>
   </PropertyGroup>
 
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+      <_Parameter1>Microsoft.CmdPal.Ext.TimeDate.UnitTests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
+
   <ItemGroup>
     <EmbeddedResource Update="Properties\Resources.resx">
       <LastGenOutput>Resources.Designer.cs</LastGenOutput>

src/modules/cmdpal/ext/Microsoft.CmdPal.Ext.WindowWalker/Microsoft.CmdPal.Ext.WindowWalker.csproj

@@ -46,4 +46,9 @@
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
   </ItemGroup>
+  <ItemGroup>
+    <AssemblyAttribute Include="System.Runtime.CompilerServices.InternalsVisibleTo">
+      <_Parameter1>Microsoft.CmdPal.Ext.WindowWalker.UnitTests</_Parameter1>
+    </AssemblyAttribute>
+  </ItemGroup>
 </Project>