[seq2seq testing] multigpu test run via subprocess (#7281)

Co-authored-by: Sam Shleifer <sshleifer@gmail.com>

examples/seq2seq/distillation.py

@@ -17,7 +17,7 @@ from finetune import main as ft_main
 from make_student import create_student_by_copying_alternating_layers, get_layers_to_supervise
 from transformers import AutoModelForSeq2SeqLM, MBartTokenizer, T5ForConditionalGeneration
 from transformers.modeling_bart import shift_tokens_right
-from utils import calculate_bleu, freeze_params, label_smoothed_nll_loss, use_task_specific_params
+from utils import calculate_bleu, check_output_dir, freeze_params, label_smoothed_nll_loss, use_task_specific_params
 
 
 # need the parent dir module
@@ -266,8 +266,7 @@ def create_module(args):
 
 def distill_main(args):
     Path(args.output_dir).mkdir(exist_ok=True)
-    if len(os.listdir(args.output_dir)) > 3 and args.do_train:
-        raise ValueError("Output directory ({}) already exists and is not empty.".format(args.output_dir))
+    check_output_dir(args, expected_items=3)
 
     model = create_module(args)
     return ft_main(args, model=model)