code: def t_est_combine(self):
      gen = np.random.RandomState(3897)
      x1 = gen.normal(size=300)
      x2 = gen.normal(size=300)
      y = x1 + x2 + gen.normal(size=300)
      x1[0:100] = np.nan
      x2[250:] = np.nan
      df = pd.DataFrame({"x1": x1, "x2": x2, "y": y})
      idata = mice.MICEData(df)
      mi = mice.MICE("y ~ x1 + x2", sm.OLS, idata, n_skip=20)
      result = mi.fit(10, 20)
  
      fmi = np.asarray([0.1778143, 0.11057262, 0.29626521])
      assert_allclose(result.frac_miss_info, fmi, atol=1e-5)
  
      params = np.asarray([-0.03486102, 0.96236808, 0.9970371])
      assert_allclose(result.params, params, atol=1e-5)
  
      tvalues = np.asarray([-0.54674776, 15.28091069, 13.61359403])
      assert_allclose(result.tvalues, tvalues, atol=1e-5)
  
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 5 for calling the TestMICE obj's underlying member method code with example usage: obj.t_est_combine() without return types