code: def test_kh_physical_diffusion():
      search_space = search.SearchSpace(
          n_agents=5,
          n_variables=2,
          lower_bound=[0, 0],
          upper_bound=[10, 10],
      )
  
      new_kh = kh.KH()
      new_kh.compile(search_space)
  
      new_physical = new_kh._physical_diffusion(1, 1, 1, 20)
  
      assert new_physical.shape == (1, 1)
  
imports: import numpy
  from opytimizer.optimizers.swarm import kh
  from opytimizer.spaces import search
label_desc: Use image node_id 13 for calling a global function with example usage: test_kh_physical_diffusion() without return types