MAINT: fix name

test/test_transaction.cpp

@@ -753,7 +753,7 @@ TEST_F(test_transaction, test_file_up_n_download) {
   ASSERT_FALSE(inserted_file.HasErrors());
 
   auto download_transaction(connection->CreateTransaction());
-  download_transaction->RetrieveAndDownloadFilesById(
+  download_transaction->RetrieveAndDownloadFileById(
     inserted_file.GetId(), test_download_file_1.string());
   download_transaction->ExecuteAsynchronously();
   ASSERT_EQ(download_transaction->WaitForIt().GetCode(), StatusCode::SUCCESS);