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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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## Detailed Description of the Pull Request / Additional comments
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## Validation Steps Performed
---------
Co-authored-by: Yu Leng <yuleng@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
What the title says. 😄
Rather than relying on the potentially overloaded `!=` or `==` operators
when checking for null, now we'll use the `is` expression (possibly
combined with the `not` operator) to ensure correct checking. Probably
overkill for many of these classes, but decided to err on the side of
consistency. Would matter more on classes that may be inherited or
extended.
Using `is` and `is not` will provide us a guarantee that no
user-overloaded equality operators (`==`/`!=`) is invoked when a
`expression is null` is evaluated.
In code form, changed all instances of:
```c#
something != null
something == null
```
to:
```c#
something is not null
something is null
```
The one exception was checking null on a `KeyChord`. `KeyChord` is a
struct which is never null so VS will raise an error when trying this
versus just providing a warning when using `keyChord != null`. In
reality, we shouldn't do this check because it can't ever be null. In
the case of a `KeyChord` it **would** be a `KeyChord` equivalent to:
```c#
KeyChord keyChord = new ()
{
Modifiers = 0,
Vkey = 0,
ScanCode = 0
};
```
Just standardizing built-in extensions to use a `internal sealed class
Icons` for all their non-dynamic icons.
Looks like a LOT of changes, but it's icons all the way down.
**WARNING:** This PR will probably blow up all in-flight PRs
at some point in the early days of CmdPal, two of us created seperate
`Exts` and `exts` dirs. Depending on what the casing was on the branch
that you checked one of those out from, it'd get stuck like that on your
PC forever.
Windows didn't care, so we never noticed.
But GitHub does care, and now browsing the source on GitHub is basically
impossible.
Closes#38081
