test: add tests for renderHtml

[evermake]

Add comprehensive tests for the render module to ensure renderHtml works correctly across various inputs and scenarios.

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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[evermake]

@cursor run ESLint to auto-fix issues

[cursor]

ESLint auto-fixed the import ordering in test/render.test.ts — the type import from ../src/types.ts now correctly comes before the external vitest import. Pushed as e8926dd.

 

[evermake]

@cursor let's make each case to start with "should ..."

[cursor]

All test case names now start with "should". All 36 tests still pass.