アイヌ語追加 (#428) (#433)

Reviewed-on: #433
Co-authored-by: miteruzo <miteruzo@naver.com>

frontend/src/test/text.tsx

@@ -0,0 +1,10 @@
+import { renderToStaticMarkup } from 'react-dom/server'
+
+import type { ReactNode } from 'react'
+
+
+export const textContentOf = (node: ReactNode): string => {
+  const container = document.createElement ('div')
+  container.innerHTML = renderToStaticMarkup (<>{node}</>)
+  return container.textContent ?? ''
+}