code: def test_convert_groups():
      n_features = 6
      grp_ptr, grp_indices = _grp_converter(3, n_features)
      np.testing.assert_equal(grp_ptr, [0, 3, 6])
      np.testing.assert_equal(grp_indices, [0, 1, 2, 3, 4, 5])
  
      grp_ptr, grp_indices = _grp_converter([1, 3, 2], 6)
      np.testing.assert_equal(grp_ptr, [0, 1, 4, 6])
      np.testing.assert_equal(grp_indices, [0, 1, 2, 3, 4, 5])
  
      groups = [[0, 2, 5], [1, 3], [4]]
      grp_ptr, grp_indices = _grp_converter(groups, 6)
      np.testing.assert_equal(grp_ptr, [0, 3, 5, 6])
      np.testing.assert_equal(grp_indices, [0, 2, 5, 1, 3, 4])
  
imports: import pytest
  import itertools
  import numpy
  from numpy.linalg import norm
  from numpy.testing import assert_allclose, assert_array_less, assert_array_equal
  from sklearn.utils.estimator_checks import check_estimator
  from sklearn.linear_model import MultiTaskLassoCV
  from sklearn.linear_model import MultiTaskLasso
  from sklearn.linear_model import lasso_path
  from celer import Lasso, GroupLasso, GroupLassoCV, MultiTaskLasso, MultiTaskLassoCV
  from celer.homotopy import celer_path, mtl_path, _grp_converter
  from celer.group_fast import dnorm_grp
  from celer.utils.testing import build_dataset
label_desc: Use image node_id 3 for calling a global function with example usage: test_convert_groups() without return types