[CmdPal][UnitTests] Add/Migrate unit test for Apps and Bookmarks extension (#41238)

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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
1. Create Apps and Bookmarks ut project.
2. Refactor Apps and Bookmarks. And some interface in these extensions
to add a abstraction layer for testing purpose.
New interface list:
* ISettingsInterface
* IUWPApplication
* IAppCache
* IBookmarkDataSource
3. Add/Migrate some test case for Apps and Bookmarks extension

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## PR Checklist

- [x] Closes: #41239 #41240
- [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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---------

Co-authored-by: Yu Leng <yuleng@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/modules/cmdpal/Tests/Microsoft.CmdPal.Ext.Apps.UnitTests/AllAppsCommandProviderTests.cs

@@ -0,0 +1,119 @@
+// 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.Linq;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace Microsoft.CmdPal.Ext.Apps.UnitTests;
+
+[TestClass]
+public class AllAppsCommandProviderTests : AppsTestBase
+{
+    [TestMethod]
+    public void ProviderHasDisplayName()
+    {
+        // Setup
+        var provider = new AllAppsCommandProvider();
+
+        // Assert
+        Assert.IsNotNull(provider.DisplayName);
+        Assert.IsTrue(provider.DisplayName.Length > 0);
+    }
+
+    [TestMethod]
+    public void ProviderHasIcon()
+    {
+        // Setup
+        var provider = new AllAppsCommandProvider();
+
+        // Assert
+        Assert.IsNotNull(provider.Icon);
+    }
+
+    [TestMethod]
+    public void TopLevelCommandsNotEmpty()
+    {
+        // Setup
+        var provider = new AllAppsCommandProvider();
+
+        // Act
+        var commands = provider.TopLevelCommands();
+
+        // Assert
+        Assert.IsNotNull(commands);
+        Assert.IsTrue(commands.Length > 0);
+    }
+
+    [TestMethod]
+    public void LookupAppWithEmptyNameReturnsNotNull()
+    {
+        // Setup
+        var mockApp = TestDataHelper.CreateTestWin32Program("Notepad", "C:\\Windows\\System32\\notepad.exe");
+        MockCache.AddWin32Program(mockApp);
+        var page = new AllAppsPage(MockCache);
+
+        var provider = new AllAppsCommandProvider(page);
+
+        // Act
+        var result = provider.LookupApp(string.Empty);
+
+        // Assert
+        Assert.IsNotNull(result);
+    }
+
+    [TestMethod]
+    public async Task ProviderWithMockData_LookupApp_ReturnsCorrectApp()
+    {
+        // Arrange
+        var testApp = TestDataHelper.CreateTestWin32Program("TestApp", "C:\\TestApp.exe");
+        MockCache.AddWin32Program(testApp);
+
+        var provider = new AllAppsCommandProvider(Page);
+
+        // Wait for initialization to complete
+        await WaitForPageInitializationAsync();
+
+        // Act
+        var result = provider.LookupApp("TestApp");
+
+        // Assert
+        Assert.IsNotNull(result);
+        Assert.AreEqual("TestApp", result.Title);
+    }
+
+    [TestMethod]
+    public async Task ProviderWithMockData_LookupApp_ReturnsNullForNonExistentApp()
+    {
+        // Arrange
+        var testApp = TestDataHelper.CreateTestWin32Program("TestApp", "C:\\TestApp.exe");
+        MockCache.AddWin32Program(testApp);
+
+        var provider = new AllAppsCommandProvider(Page);
+
+        // Wait for initialization to complete
+        await WaitForPageInitializationAsync();
+
+        // Act
+        var result = provider.LookupApp("NonExistentApp");
+
+        // Assert
+        Assert.IsNull(result);
+    }
+
+    [TestMethod]
+    public void ProviderWithMockData_TopLevelCommands_IncludesListItem()
+    {
+        // Arrange
+        var provider = new AllAppsCommandProvider(Page);
+
+        // Act
+        var commands = provider.TopLevelCommands();
+
+        // Assert
+        Assert.IsNotNull(commands);
+        Assert.IsTrue(commands.Length >= 1); // At least the list item should be present
+    }
+}