code: def test_numpy(self):
      results = tools._ensure_2d(self.ndarray)
      assert_array_equal(results[0], self.ndarray)
      assert_equal(results[1], None)
  
      results = tools._ensure_2d(self.ndarray[:, 0])
      assert_array_equal(results[0], self.ndarray[:, [0]])
      assert_equal(results[1], None)
  
imports: from statsmodels.compat.pandas import assert_frame_equal, assert_series_equal
  from statsmodels.compat.python import lrange
  import string
  import numpy
  from numpy.random import standard_normal
  from numpy.testing import assert_almost_equal, assert_array_equal, assert_equal, assert_string_equal
  import pandas
  import pytest
  from statsmodels.datasets import longley
  from statsmodels.tools import tools
  from statsmodels.tools.tools import pinv_extended
label_desc: Use image node_id 4 for calling the TestEnsure2d obj's underlying member method code with example usage: obj.test_numpy() without return types