Improve test hack

Author: schmidt-sebastian

packages/firestore/src/local/simple_db.ts

@@ -277,11 +277,18 @@ export class SimpleDb {
         // make this a test-only setting.
         // // Horrible hack to verify that idempotent functions can be run more
         // // than once.
-        // const transactionFnResult = (idempotent && attemptNumber === 1
-        //   ? transactionFn(transaction)
-        //   : PersistencePromise.resolve({} as T)
-        // ).next(() => transactionFn(transaction))
         const transactionFnResult = transactionFn(transaction)
+          // TODO(schmidt-sebastian): Remove this code/comment or find a way to
+          // make this a test-only setting.
+          // // Horrible hack to verify that idempotent functions can be run more
+          // // than once.
+          //   .next(result => {
+          //     if (idempotent && attemptNumber == 1) {
+          //       class DOMException {}
+          //       throw new DOMException();
+          //     }
+          //     return result;
+          //   })
           .catch(error => {
             // Abort the transaction if there was an error.
             transaction.abort(error);