code: def test_get_force():
      charges = np.array([[1.0, 0, 0], [0, 1.0, 0], [0, 0, 1.0]])
      force, pot = _get_forces(charges)
      nt.assert_array_almost_equal(force, 0)
  
      charges = np.array([[1, -0.1, 0], [1, 0, 0]])
      force, pot = _get_forces(charges)
      nt.assert_array_almost_equal(force[1, [0, 2]], 0)
      nt.assert_(force[1, 1] > 0)
  
imports: import numpy
  import numpy.testing
  import pytest
  import warnings
  from dipy.core.sphere import Sphere, HemiSphere, unique_edges, unique_sets, faces_from_sphere_vertices, disperse_charges, fibonacci_sphere, disperse_charges_alt, _get_forces, _get_forces_alt, unit_octahedron, unit_icosahedron, hemi_icosahedron
  from dipy.core.geometry import cart2sphere, vector_norm
  from dipy.core.sphere_stats import random_uniform_on_sphere
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 19 for calling a global function with example usage: test_get_force() without return types