code: def test_fillna_datetime64(self, tz):
      # GH 11343
      idx = pd.DatetimeIndex(
          ["2011-01-01 09:00", pd.NaT, "2011-01-01 11:00"]
      )
  
      exp = pd.DatetimeIndex(
          ["2011-01-01 09:00", "2011-01-01 10:00", "2011-01-01 11:00"]
      )
      tm.assert_index_equal(
          idx.fillna(pd.Timestamp("2011-01-01 10:00")), exp
      )
  
      # tz mismatch
      exp = pd.Index(
          [
              pd.Timestamp("2011-01-01 09:00"),
              pd.Timestamp("2011-01-01 10:00", tz=tz),
              pd.Timestamp("2011-01-01 11:00"),
          ],
          dtype=object,
      )
      tm.assert_index_equal(
          idx.fillna(pd.Timestamp("2011-01-01 10:00", tz=tz)), exp
      )
  
      # object
      exp = pd.Index(
          [
              pd.Timestamp("2011-01-01 09:00"),
              "x",
              pd.Timestamp("2011-01-01 11:00"),
          ],
          dtype=object,
      )
      tm.assert_index_equal(idx.fillna("x"), exp)
  
      idx = pd.DatetimeIndex(
          ["2011-01-01 09:00", pd.NaT, "2011-01-01 11:00"], tz=tz
      )
  
      exp = pd.DatetimeIndex(
          ["2011-01-01 09:00", "2011-01-01 10:00", "2011-01-01 11:00"],
          tz=tz,
      )
      tm.assert_index_equal(
          idx.fillna(pd.Timestamp("2011-01-01 10:00", tz=tz)), exp
      )
  
      exp = pd.Index(
          [
              pd.Timestamp("2011-01-01 09:00", tz=tz),
              pd.Timestamp("2011-01-01 10:00"),
              pd.Timestamp("2011-01-01 11:00", tz=tz),
          ],
          dtype=object,
      )
      tm.assert_index_equal(
          idx.fillna(pd.Timestamp("2011-01-01 10:00")), exp
      )
  
      # object
      exp = pd.Index(
          [
              pd.Timestamp("2011-01-01 09:00", tz=tz),
              "x",
              pd.Timestamp("2011-01-01 11:00", tz=tz),
          ],
          dtype=object,
      )
      tm.assert_index_equal(idx.fillna("x"), exp)
  
imports: import pytest
  import pandas
  import pandas._testing
label_desc: Use image node_id 1 for calling the TestDatetimeIndexFillNA obj's underlying member method code with example usage: obj.test_fillna_datetime64(tz) without return types