code: def test_x0_input(rng):
      for x0 in [6, 7, 12, "Rigid", "rigid", "similarity", "Affine"]:
          StreamlineLinearRegistration(x0=x0)
  
      for x0 in [rng.random(6), rng.random(7), rng.random(12)]:
          StreamlineLinearRegistration(x0=x0)
  
      for x0 in [
          8,
          20,
          "Whatever",
          rng.random(20),
          rng.random((20, 3)),
      ]:
          assert_raises(ValueError, StreamlineLinearRegistration, x0=x0)
  
      x0 = rng.random((4, 3))
      assert_raises(ValueError, StreamlineLinearRegistration, x0=x0)
  
      x0_6 = np.zeros(6)
      x0_7 = np.array([0, 0, 0, 0, 0, 0, 1.0])
      x0_12 = np.array([0, 0, 0, 0, 0, 0, 1.0, 1.0, 1.0, 0, 0, 0])
  
      x0_s = [x0_6, x0_7, x0_12, x0_6, x0_7, x0_12]
  
      for i, x0 in enumerate(
          [6, 7, 12, "Rigid", "similarity", "Affine"]
      ):
          slr = StreamlineLinearRegistration(x0=x0)
          assert_equal(slr.x0, x0_s[i])
  
imports: import numpy
  from numpy.testing import assert_, assert_equal, assert_almost_equal, assert_array_almost_equal, assert_raises
  from dipy.align.streamlinear import compose_matrix44, decompose_matrix44, BundleSumDistanceMatrixMetric, BundleMinDistanceMatrixMetric, BundleMinDistanceMetric, StreamlineLinearRegistration, StreamlineDistanceMetric, groupwise_slr, get_unique_pairs
  from dipy.tracking.streamline import center_streamlines, unlist_streamlines, relist_streamlines, transform_streamlines, set_number_of_points, Streamlines
  from dipy.io.streamline import load_tractogram
  from dipy.core.geometry import compose_matrix
  from dipy.data import get_fnames, two_cingulum_bundles, read_five_af_bundles
  from dipy.align.bundlemin import _bundle_minimum_distance_matrix, _bundle_minimum_distance, distance_matrix_mdf
  from dipy.testing.decorators import set_random_number_generator
label_desc: Use image node_id 19 for calling a global function with example usage: test_x0_input(rng) without return types