code: def test_invalid_alpha(self):
      with pytest.raises(ValueError):
          MixUpSoftLabelDataset(
              self.siamese_dataset, self.n_class, alpha=self.alpha - 5.0
          )
  
file_path: chainercv/tests/datasets_tests/test_mixup_soft_label_dataset.py
imports: import unittest
  import numpy
  import pytest
  from chainer import testing
  from chainer.datasets import TupleDataset
  from chainercv.datasets import MixUpSoftLabelDataset
  from chainercv.datasets import SiameseDataset
  from chainercv.utils.testing.assertions.assert_is_image import assert_is_image
label_desc: Use image node_id 4 for calling the TestMixupSoftLabelDataset obj's underlying member method code with example usage: obj.test_invalid_alpha() without return types