[test] stringify errors

Author: avivkeller

packages/rehype-shiki/src/index.mjs

@@ -24,6 +24,8 @@ const { shiki, getLanguageDisplayName, highlightToHast, highlightToHtml } =
       transformerTwoslash({
         langs: ['ts', 'js', 'cjs', 'mjs'],
         // throws: false,
+        onTwoslashError: error => JSON.stringify(error),
+        onShikiError: error => JSON.stringify(error),
       }),
     ],
     // We use the faster WASM engine on the server instead of the web-optimized version.