Fix sampler test (#1379)

tests/samplers/test_sampler.py

 # pylint: disable=protected-access
-import pytest
 import random
 from typing import Tuple
 from unittest.mock import patch
 
+import pytest
 import torch
 
 from vllm.model_executor.layers.sampler import Sampler
@@ -69,7 +69,7 @@ def test_sampler_all_greedy(seed: int):
                              input_metadata=input_metadata)
     expected = torch.argmax(fake_logits, dim=-1)
     for i, sequence_output in enumerate(sampler_output):
-        for nth_output in sequence_output:
+        for nth_output in sequence_output.samples:
             assert nth_output.output_token == expected[i].item()
 
 
@@ -101,7 +101,7 @@ def test_sampler_all_random(seed: int):
                              hidden_states=input_tensor,
                              input_metadata=input_metadata)
     for i, sequence_output in enumerate(sampler_output):
-        for nth_output in sequence_output:
+        for nth_output in sequence_output.samples:
             assert nth_output.output_token == i
 
 
@@ -181,5 +181,5 @@ def test_sampler_mixed(seed: int):
     for i, sequence_output in enumerate(sampler_output):
         if seq_group_metadata_list[i].sampling_params.use_beam_search:
             continue
-        for nth_output in sequence_output:
+        for nth_output in sequence_output.samples:
             assert nth_output.output_token in expected_tokens