Is there an existing issue for this?

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• I have read the guide to filing a bug

Steps to reproduce

While working on some other M3 date picker issues like #126597, I noticed the M3 layout and config changes made in #119033 aren't tested in date_picker_test.dart.

https://github.com/flutter/flutter/pull/119033/files#diff-198d5dd0fe89bb71e1940816baf20e7b57ee896ed31120b7c3fcebcc4ac3bfbe has a bunch of changes in date_picker.dart and most of these changes aren't tested in date_picker_test.dart.

Expected results

date_picker_test.dart has M3 test coverage

Actual results

Most of the M3 changes aren't tested and modifying some M3 defaults or removing M3-related widgets from date_picker.test doesn't fail tests in the date_picker_test.dart class.

Code sample

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