code: def test_single(self):
      num_of_data = 100
      data = DatasetWithVaryLength(num_of_data)
      sampler = UnrepeatedSequentialSampler(data, length=data.data)
      indexes = list(sampler)
      assert indexes == list(range(num_of_data))
  
file_path: fastNLP/tests/core/samplers/test_unrepeated_sampler.py
imports: from itertools import chain
  import pytest
  from fastNLP.core.samplers import UnrepeatedRandomSampler, UnrepeatedSortedSampler, UnrepeatedSequentialSampler
label_desc: Use image node_id 1 for calling the TestUnrepeatedSequentialSampler obj's underlying member method code with example usage: obj.test_single() without return types