fix: use original require() error for TS files if ERR_UNKNOWN_FILE_EXTENSION

lib/nodejs/esm-utils.js

@@ -92,9 +92,19 @@ const tryImportAndRequire = async (file, esmDecorator) => {
 const requireModule = async (file, esmDecorator) => {
   try {
     return require(file);
-  } catch (err) {
-    // Import if require fails.
-    return dealWithExports(await formattedImport(file, esmDecorator));
+  } catch (requireErr) {
+    // Fallback to import() if require() fails.
+    try {
+      return dealWithExports(await formattedImport(file, esmDecorator));
+    } catch (importErr) {
+      // If a --require module throws in a Node.js version that doesn't yet support .ts files,
+      // the fallback import() will throw an uninformative error about the file extension.
+      // What we actually care about is the original require() error.
+      // See: https://github.com/mochajs/mocha/issues/5393
+      throw /\.(?:c|m)?ts$/.test(file) || importErr?.code === "ERR_UNKNOWN_FILE_EXTENSION"
+        ? requireErr
+        : importErr;
+    }
   }
 }