When using the generator with the script format :

generator-name [params] > test-index

eg : gen_rnd 1 100 0 1000 > 1

The test case files get generated.

But when using script format to generate multiple files :

generator-name [params] > {test-indices}

eg : gen_rnd 1 100 0 1000 > {1-2}

The test case file show an error :