[cj-radcliff]

Description

(Stacked on #9209 / ui-test-harness-iu262)

Adds five core IDE Starter UI tests against IntelliJ IDEA 2026.2.3 covering project creation, pubspec.yaml dependency fetching, widget test execution, refactoring, and live templates:

• NewProjectIU262UITest:
  • Exercises the Welcome screen's New Project wizard (Flutter generator) on IntelliJ IDEA 2026.2.3, verifies the generated project opens and finishes indexing, and cleans up the project directory afterwards.
• PubGetUITest:
  • Opens an existing Flutter project, adds http: ^1.2.0 to pubspec.yaml, invokes Flutter Pub Get (flutter.pub.get), and verifies pubspec.lock (direct main hosted dependency), .dart_tool/package_config.json, and the downloaded package in the pub cache (lib/http.dart).
• RunWidgetTestUITest:
  • Opens test/widget_test.dart, places the caret on testWidgets, invokes RunClass from the editor, and verifies the IDE test runner reports the widget test passed.
• ExtractWidgetUITest:
  • Opens lib/main.dart, places the caret on Text('You have pushed...'), invokes Extract Flutter Widget... (Flutter.ExtractWidget), enters CounterLabel, and verifies class CounterLabel extends StatelessWidget is extracted cleanly.
• StatelessWidgetLiveTemplateUITest:
  • Opens lib/greeting.dart, types stless + Tab + Greeting, and verifies the live template expands into class Greeting extends StatelessWidget with const Greeting({super.key});.
• testSrc/integration/README.md:
  • Adds the Available tests table and updates the example command to RunWidgetTestUITest.

Verification

• Verified compileIntegrationKotlin compiles cleanly.
• Verified all 5 UI tests pass against IntelliJ IDEA 2026.2.3 (./gradlew --no-daemon integration --tests io.flutter.integrationTest.<TestClass>).

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Review the contribution guidelines below:

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.
• I've included the required information in the description above.
• My up-to-date information is in the AUTHORS file.
• I've updated CHANGELOG.md if appropriate.

[gemini-code-assist]

Code Review

This pull request adds a suite of UI integration tests for the Flutter IntelliJ plugin, covering widget extraction, project creation, running pub get, widget testing, and live templates, along with updated documentation. The feedback points out a violation of the Kotlin style guide in PubGetUITest.kt where the double-bang (!!) operator is used, and suggests replacing it with checkNotNull for better safety and error context.

[gemini-code-assist]

[MUST-FIX] Avoid using the double-bang !! operator as per the Kotlin style guide. Use checkNotNull or an Elvis operator with an explicit error message instead to ensure null safety and provide better error context.

Suggested change

	val lockEntry = lockEntry()!!
	val lockEntry = checkNotNull(lockEntry()) { "pubspec.lock entry for $PACKAGE not found" }

References

1. Null Safety: NEVER use the double-bang !! operator. Use ?., ?:, or if (x != null). ^(link)