[material_ui] Enable chip_test

[elliette]

Port over chip_test from flutter/flutter#184279

Work towards flutter/flutter#182636 and flutter/flutter#188395

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
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• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
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• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

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[gemini-code-assist]

Code Review

This pull request removes @Skip annotations from several test files, reorganizes imports, and extracts the findByTooltip finder and FeedbackTester helper into standalone test utility files (finders.dart and feedback_tester.dart) to resolve cross-import issues. Feedback is provided to use optional chaining instead of a null assertion operator on widget.richMessage in finders.dart to avoid potential runtime exceptions.

[gemini-code-assist]

Code Review

This pull request removes the @Skip annotation from chip_test.dart, fixes cross-imports by updating relative paths, and wraps a thrown multiline string in an Exception object. The review feedback suggests refactoring the multiline string exception message to avoid preserving accidental leading whitespace, recommending adjacent string literals with explicit newlines instead.

[gemini-code-assist]

The multiline string literal preserves the leading whitespace (14 spaces) on each line, which will make the exception message heavily indented and hard to read in test failure logs.

Using adjacent string literals with explicit \n avoids accidental leading whitespace while keeping the code clean and readable.

    throw Exception(
      'Expected: center == $expectedCenter, radius == $expectedRadius\n'
      'Found: center == $center radius == $radius',
    );

[Piinks]

LGTM! Thank you!