Inspector integration tests are resilient to Flutter framework changes

[elliette]

Work towards flutter/flutter#172037

Our current inspector integration test is quite brittle, since the test cases for the inspector tree assume the implementation widgets from the Flutter frameworks will be in a consistent order. This PR removes that assumption to make sure the inspector tests won't fail due to framework changes.

This PR:

• Adds a custom widget library (named custom_widgets ) to our test fixtures which contains a few simple "custom" widgets
• Adds a new test app (named inspector_app) to our test fixtures which uses the widgets from the custom_widgets library instead of from the Framework
• Updates inspector_v2/inspector_integration_test to use the new inspector_app

This way we can rely on the implementing widgets from custom_widgets remaining consistent. However, since those are implemented using widgets from the framework, I have skipped any golden comparisons when implementation widgets are visible in the tree.

Note: We are planning on removing the legacy inspector (integration test is packages/devtools_app/test/screens/inspector/inspector_integration_test.dart) soon now that ~99% of users are using the new inspector. Therefore, for the legacy inspector integration test, I simply skipped any golden comparisons for the details tree.

[justinmc]

LGTM from my side 👍. Just some questions below.

I wonder how many users of the framework end up doing similar things.

[justinmc]

I wonder what you guys were hoping to test with these goldens and if it can be achieved with widget tests instead?

Taking a look at a golden image here (https://github.com/flutter/devtools/blob/master/packages/devtools_app/test/test_infra/goldens/integration_inspector_select_center_details_tree.png) it looks pretty UI-light, which is generally better for golden testing, but still I usually avoid golden testing if possible due to unintended breakages like this.

[elliette]

Yes, the golden tests are mostly to make sure that we don't accidentally introduce some UI change that we wouldn't have thought to test in our widget tests. Since this specific view will be going away, I'm not too concerned about not having comprehensive test coverage.

[elliette]

For the V2 view, I think the fact that we have golden tests for the panel (just without implementation widgets enabled) should catch the vast majority of UI regressions.

[justinmc]

So you are working around the fact that Flutter might make breaking changes to these widgets? On the framework team we're currently thinking about what widgets should be in the Widgets library (and more stable), so maybe this helps inform us there.

I'm seeing that you made replacements for these widgets:

• MaterialApp
• Container
• Center
• Text
• TextButton

[elliette]

Yes, exactly! If there are widgets in the Widgets library that are guaranteed to be stable that would be good to know, since we could make sure our app only contains those widgets.