### What problem does this PR solve?

Add license statement.

### Type of change

- [x] Refactoring

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

### What problem does this PR solve?

Fix errors detected by Ruff

### Type of change

- [x] Refactoring

### What problem does this PR solve?

Add tests for frontend API

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>