code: def test_D_star_vp():
      """
      Test if the `IvimFit` class returns the correct D_star
      """
      ivim_fit_VP = ivim_model_VP.fit(data_single)
      assert_array_almost_equal(
          ivim_fit_VP.D_star, D_star_VP, decimal=4
      )
  
imports: import warnings
  import numpy
  from numpy.testing import assert_array_equal, assert_array_almost_equal, assert_raises, assert_array_less, assert_, assert_equal
  from dipy.testing import assert_greater_equal
  import pytest
  from dipy.reconst.ivim import ivim_prediction, IvimModel
  from dipy.core.gradients import gradient_table, generate_bvecs
  from dipy.sims.voxel import multi_tensor
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 26 for calling a global function with example usage: test_D_star_vp() without return types