test(rspack_util): add test cases

[ycjcl868]

Summary

Related issue (if exists)

Types of changes

• Docs change / Dependency upgrade
• Bug fix
• New feature / Improvement
• Refactoring
• Breaking change

Checklist

• I have added changeset via pnpm run changeset.
• I have added tests to cover my changes.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9316e6f

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[ycjcl868]

According to the previous test cases, will they be added later?

https://github.com/webpack/webpack/blob/4b4ca3bb53f36a5b8fc6bc1bd976ed7af161bd80/test/identifier.unittest.js#L8

[hardfist]

thank you, adding rust unittest is very helpful