text: import numpy as np
  import pytest
  
  from pandas import DatetimeIndex, Series, date_range
  import pandas._testing as tm
  
  
  class TestTZConvert:
      def test_series_tz_convert(self):
          rng = date_range("1/1/2011", periods=200, freq="D", tz="US/Eastern")
          ts = Series(1, index=rng)
  
          result = ts.tz_convert("Europe/Berlin")
          assert result.index.tz.zone == "Europe/Berlin"
  
          # can't convert tz-naive
          rng = date_range("1/1/2011", periods=200, freq="D")
          ts = Series(1, index=rng)
  
          with pytest.raises(TypeError, match="Cannot convert tz-naive"):
              ts.tz_convert("US/Eastern")
  
      def test_series_tz_convert_to_utc(self):
          base = DatetimeIndex(["2011-01-01", "2011-01-02", "2011-01-03"], tz="UTC")
          idx1 = base.tz_convert("Asia/Tokyo")[:2]
          idx2 = base.tz_convert("US/Eastern")[1:]
  
          res = Series([1, 2], index=idx1) + Series([1, 1], index=idx2)
          tm.assert_series_equal(res, Series([np.nan, 3, np.nan], index=base))
  