code: def test_predict_custom_index():
      np.random.seed(328423)
      endog = pd.DataFrame(np.random.normal(size=50))
      mod = structural.UnobservedComponents(endog, "llevel")
      res = mod.smooth(mod.start_params)
      out = res.predict(start=1, end=1, index=["a"])
      assert_equal(out.index.equals(pd.Index(["a"])), True)
  
imports: import warnings
  import numpy
  from numpy.testing import assert_equal, assert_allclose, assert_raises
  import pandas
  import pytest
  from statsmodels.datasets import macrodata
  from statsmodels.tools.sm_exceptions import SpecificationWarning
  from statsmodels.tsa.statespace import structural
  from statsmodels.tsa.statespace.structural import UnobservedComponents
  from statsmodels.tsa.statespace.tests.results import results_structural
label_desc: Use image node_id 26 for calling a global function with example usage: test_predict_custom_index() without return types