code: def test_sigmoid(self):
      self.assertEqual(0, sigmoid(-np.inf))
      self.assertEqual(0.5, sigmoid(0))
      self.assertEqual(1, sigmoid(np.inf))
  
      self.assertGreater(0.5, sigmoid(-0.1))
      self.assertGreater(sigmoid(0.1), 0.5)
  
imports: import unittest
  import numpy
  import numpy.testing
  import scipy.sparse
  from cornac.utils.common import sigmoid
  from cornac.utils.common import safe_indexing
  from cornac.utils.common import validate_format
  from cornac.utils.common import scale
  from cornac.utils.common import clip
  from cornac.utils.common import excepts
  from cornac.utils.common import intersects
  from cornac.utils.common import estimate_batches
  from cornac.utils.common import get_rng
  from cornac.utils.common import normalize
label_desc: Use image node_id 1 for calling the TestCommon obj's underlying member method code with example usage: obj.test_sigmoid() without return types