code: def test_leastsq_error():
      """
      Test error handling of the `_leastsq` method works when unfeasible x0 is
      passed. If an unfeasible x0 value is passed using which leastsq fails, the
      x0 value is returned as it is.
      """
      with warnings.catch_warnings(record=True) as w:
          warnings.simplefilter("always", category=UserWarning)
          fit = ivim_model_trr._leastsq(data_single, [-1, -1, -1, -1])
          assert_greater_equal(len(w), 1)
          assert_(issubclass(w[-1].category, UserWarning))
          assert_("" in str(w[-1].message))
          assert_("x0 is unfeasible" in str(w[-1].message))
  
      assert_array_almost_equal(fit, [-1, -1, -1, -1])
  
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 24 for calling a global function with example usage: test_leastsq_error() without return types