code: def test_design_matrix():
      ub = unique_bvals_magnitude(bvals_3s)
      D = msdki.design_matrix(ub)
      Dgt = np.ones((4, 3))
      Dgt[:, 0] = -ub
      Dgt[:, 1] = 1.0 / 6 * ub**2
      assert_array_almost_equal(D, Dgt)
  
file_path: dipy/dipy/reconst/tests/test_msdki.py
imports: import numpy
  import random
  from numpy.testing import assert_array_almost_equal, assert_raises, assert_almost_equal, assert_
  from dipy.sims.voxel import single_tensor, multi_tensor_dki
  from dipy.io.gradients import read_bvals_bvecs
  from dipy.core.gradients import gradient_table, unique_bvals_magnitude, round_bvals
  from dipy.data import get_fnames
  import dipy.reconst.msdki
  from dipy.reconst.msdki import msk_from_awf, awf_from_msk
label_desc: Use image node_id 5 for calling a global function with example usage: test_design_matrix() without return types