code: def test_from_6x1_to_3x3():
      """Test conversion from Voigt notation."""
      V = np.arange(1, 7)[:, np.newaxis].astype(float)
      T = np.array(
          (
              [1, 4.24264069, 3.53553391],
              [4.24264069, 2, 2.82842712],
              [3.53553391, 2.82842712, 3],
          )
      )
      npt.assert_array_almost_equal(qti.from_6x1_to_3x3(V), T)
      npt.assert_array_almost_equal(
          qti.from_6x1_to_3x3(qti.from_3x3_to_6x1(T)), T
      )
      npt.assert_raises(ValueError, qti.from_6x1_to_3x3, T)
  
imports: import numpy
  import numpy.testing
  import dipy.reconst.qti
  from dipy.core.gradients import gradient_table
  from dipy.sims.voxel import vec2vec_rotmat
  from dipy.core.sphere import disperse_charges, HemiSphere
  from dipy.reconst.dti import fractional_anisotropy
  from dipy.testing.decorators import set_random_number_generator
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 2 for calling a global function with example usage: test_from_6x1_to_3x3() without return types