test(web): add unit tests for Avatar component

[SherlockShemol]

Closes #30200

Added comprehensive tests for the Avatar component covering:

• Rendering with image URL vs fallback initial
• Size, className, and textClassName props
• Image load error handling and state recovery
• Edge cases like empty names, CJK characters, zero/large sizes

All tests pass locally. Should help catch regressions when touching this component.

[gemini-code-assist]

Summary of Changes

Hello @SherlockShemol, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the stability of the Avatar component by introducing a comprehensive suite of unit tests. These tests validate the component's rendering logic, prop handling, image loading error recovery, and behavior under various edge conditions, aiming to prevent future regressions and ensure consistent functionality.

Highlights

• Comprehensive Unit Tests: Added a new test file (index.spec.tsx) to provide extensive unit test coverage for the Avatar component, ensuring its reliability and preventing regressions.
• Rendering Scenarios: Tests now cover how the Avatar component renders with a valid image URL versus falling back to an initial character when no image is provided.
• Prop Validation: Validated the correct application of size, className, and textClassName props, ensuring they modify the component's appearance as expected in various scenarios.
• Image Error Handling: Implemented tests for image load error handling, including scenarios where an image fails to load, how the component recovers, and how the error state is managed upon prop changes.
• Edge Case Coverage: Addressed various edge cases such as empty names, names containing CJK characters, empty string avatars, and extreme size values (zero or very large) to ensure robust behavior.

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[gemini-code-assist]

Code Review

This pull request introduces a comprehensive suite of unit tests for the Avatar component using React Testing Library and Vitest. The tests cover a wide range of scenarios, including rendering logic, prop handling, state management for image loading errors, event handlers, and various edge cases. The test suite is well-structured and thorough, which will be very valuable for ensuring the component's stability and preventing future regressions. I have one suggestion to improve the robustness of a test by adhering to a testing-library best practice.