code: def test_multiple_b0():
      # Generate a signal with multiple b0
  
      # This gives an isotropic signal.
      signal = multi_tensor(
          gtab_with_multiple_b0,
          mevals,
          snr=None,
          S0=S0,
          fractions=[f * 100, 100 * (1 - f)],
      )
      # Single voxel data
      data_single = signal[0]
  
      msg = "Bounds for this fit have been set from experiments .*"
      with warnings.catch_warnings():
          warnings.filterwarnings(
              "ignore", message=msg, category=UserWarning
          )
          ivim_model_multiple_b0 = IvimModel(
              gtab_with_multiple_b0, fit_method="trr"
          )
  
      ivim_model_multiple_b0.fit(data_single)
  
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 13 for calling a global function with example usage: test_multiple_b0() without return types