code: def test_bso_sigmoid():
      new_bso = bso.BSO()
  
      x = 0.5
  
      y = new_bso._sigmoid(x)
  
      assert y == 0.6224593312018546
  
file_path: opytimizer/tests/opytimizer/optimizers/social/test_bso.py
imports: import numpy
  from opytimizer.optimizers.social import bso
  from opytimizer.spaces import search
label_desc: Use image node_id 4 for calling a global function with example usage: test_bso_sigmoid() without return types