Describe the bug
If an external tool (like some AI tool) creates a new unit test file, it does not appear in the Testing tab automatically.

To Reproduce

1. Create a new app
   flutter create flutter_app_3_35_3
2. Open the project folder in VS Code and open the Testing tab to see tests.
3. In the integrated Terminal, create a new test file:
   touch test/foo_test.dart

Expected behavior
The new test file appears in the Testing tab.

Actual behavior
The new test file does not appear in the Testing tab until you open it in the editor first.

Environment
Operating System and version: macos / Version 15.5 (Build 24F74) darwin-arm64
VS Code version: mac 1.103.2
Dart Code extension: 3.118.1
Flutter extension: 3.118.0
Dart/Flutter SDK version: Dart 3.9.2 / Flutter 3.35.3