code: def test_next_sample(self):
      df = gendat()
      imp_data = mice.MICEData(df)
  
      all_x = []
      for j in range(2):
          x = imp_data.next_sample()
          assert isinstance(x, pd.DataFrame)
          assert_equal(df.shape, x.shape)
          all_x.append(x)
  
      # The returned dataframes are all the same object
      assert all_x[0] is all_x[1]
  
imports: import numpy
  import pandas
  import pytest
  from statsmodels.imputation import mice
  import statsmodels.api
  from numpy.testing import assert_equal, assert_allclose
  import warnings
label_desc: Use image node_id 3 for calling the TestMICEData obj's underlying member method code with example usage: obj.test_next_sample() without return types