code: def test_ensure2d():
      s = Series([1, 2, 3], name="x")
      df = ensure2d(s, "x")
      assert isinstance(df, DataFrame)
  
      df2 = ensure2d(df, "x")
      assert df is df2
  
      npa = ensure2d(s.values, "x")
      assert isinstance(npa, np.ndarray)
      assert npa.ndim == 2
  
      npa = ensure2d(np.array(1.0), "x")
      assert isinstance(npa, np.ndarray)
      assert npa.ndim == 2
  
      with pytest.raises(ValueError):
          ensure2d(np.array([[[1]]]), "x")
      with pytest.raises(TypeError):
          ensure2d([1], "x")
  
imports: from abc import abstractmethod
  import datetime
  import numpy
  from numpy.random import RandomState
  from numpy.testing import assert_equal
  from pandas import DataFrame, Series, Timedelta, date_range
  import pytest
  from arch import doc
  from arch.univariate.base import implicit_constant
  from arch.utility.array import ConcreteClassMeta, DocStringInheritor, cutoff_to_index, date_to_index, ensure1d, ensure2d, find_index, parse_dataframe
label_desc: Use image node_id 3 for calling a global function with example usage: test_ensure2d() without return types