code: def test_estimate_f_D_star():
      """
      Test if the `estimate_f_D_star` returns the correct parameters after a
      non-linear fit.
      """
      params_f_D = f + 0.001, D + 0.0001
      assert_array_almost_equal(
          ivim_model_trr.estimate_f_D_star(
              params_f_D, data_single, S0, D
          ),
          (f, D_star),
      )
  
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 21 for calling a global function with example usage: test_estimate_f_D_star() without return types