code: def test_mean():
      distribution = ElectronSampler(
          np.array([[1, 1, 3], [3, 2, 3]]), f
      )
      x1 = np.array([[[[1, 2, 3]]], [[[4, 5, 6]]]])
      mean = distribution.harmonic_mean(x1)
      assert (
          mean
          == np.array(
              [[[[1.3333333333333333]]], [[[4.988597077109626]]]]
          )
      ).all()
  
imports: import numpy
  from deepchem.utils.electron_sampler import ElectronSampler
label_desc: Use image node_id 2 for calling a global function with example usage: test_mean() without return types