code: def test_min_signal_default(self):
      signal, gtab, expected = make_fake_signal()
  
      with warnings.catch_warnings():
          warnings.filterwarnings(
              "ignore",
              message=descoteaux07_legacy_msg,
              category=PendingDeprecationWarning,
          )
  
          model_default = self.model(gtab, 4)
  
      shm_default = model_default.fit(signal).shm_coeff
  
      with warnings.catch_warnings():
          warnings.filterwarnings(
              "ignore",
              message=descoteaux07_legacy_msg,
              category=PendingDeprecationWarning,
          )
  
          model_correct = self.model(gtab, 4, min_signal=1e-5)
  
      shm_correct = model_correct.fit(signal).shm_coeff
      assert_equal(shm_default, shm_correct)
  
imports: import warnings
  import numpy
  import numpy.linalg
  import numpy.testing
  from dipy.testing import assert_true
  from numpy.testing import assert_array_equal, assert_array_almost_equal, assert_equal, assert_raises
  from scipy.special import sph_harm
  from dipy.core.sphere import hemi_icosahedron, Sphere
  from dipy.core.gradients import gradient_table
  from dipy.core.interpolation import NearestNeighborInterpolator
  from dipy.sims.voxel import single_tensor
  from dipy.direction.peaks import peak_directions
  from dipy.reconst.shm import sf_to_sh, sh_to_sf
  from dipy.sims.voxel import multi_tensor_odf
  from dipy.data import mrtrix_spherical_functions
  from dipy.reconst import odf
  from dipy.reconst.shm import real_sh_descoteaux_from_index, real_sym_sh_basis, real_sym_sh_mrtrix, real_sh_descoteaux, real_sh_tournier, sph_harm_ind_list, order_from_ncoef, OpdtModel, normalize_data, hat, lcr_matrix, smooth_pinv, bootstrap_data_array, bootstrap_data_voxel, ResidualBootstrapWrapper, CsaOdfModel, QballModel, SphHarmFit, spherical_harmonics, anisotropic_power, calculate_max_order, sh_to_sf_matrix, gen_dirac, convert_sh_to_full_basis, convert_sh_from_legacy, convert_sh_to_legacy, convert_sh_descoteaux_tournier, descoteaux07_legacy_msg, tournier07_legacy_msg
label_desc: Use image node_id 5 for calling the TestQballModel obj's underlying member method code with example usage: obj.test_min_signal_default() without return types