code: def test_ensure_output_format_returns_dense_from_dense_if_required(
      self,
  ):
      classifier = ProblemTransformationBase(require_dense=True)
  
      y = np.zeros((2, 3))
      ensured_y = classifier._ensure_output_format(y)
  
      self.assertTrue(not sp.issparse(ensured_y))
      self.ensure_output_spaces_contain_the_same_data(y, ensured_y)
  
imports: import itertools
  import unittest
  import numpy
  import scipy.sparse
  from builtins import range
  from builtins import zip
  from sklearn.base import BaseEstimator
  from .test_utils import SPARSE_MATRIX_FORMATS
  from ..base import ProblemTransformationBase
label_desc: Use image node_id 18 for calling the ProblemTransformationBaseTest obj's underlying member method code with example usage: obj.test_ensure_output_format_returns_dense_from_dense_if_required() without return types