code: def test_zfill(any_string_dtype):
      s = Series(
          ["1", "22", "aaa", "333", "45678"], dtype=any_string_dtype
      )
  
      result = s.str.zfill(5)
      expected = Series(
          ["00001", "00022", "00aaa", "00333", "45678"],
          dtype=any_string_dtype,
      )
      tm.assert_series_equal(result, expected)
      expected = np.array(
          [v.zfill(5) for v in np.array(s)], dtype=np.object_
      )
      tm.assert_numpy_array_equal(
          np.array(result, dtype=np.object_), expected
      )
  
      result = s.str.zfill(3)
      expected = Series(
          ["001", "022", "aaa", "333", "45678"], dtype=any_string_dtype
      )
      tm.assert_series_equal(result, expected)
      expected = np.array(
          [v.zfill(3) for v in np.array(s)], dtype=np.object_
      )
      tm.assert_numpy_array_equal(
          np.array(result, dtype=np.object_), expected
      )
  
      s = Series(
          ["1", np.nan, "aaa", np.nan, "45678"], dtype=any_string_dtype
      )
      result = s.str.zfill(5)
      expected = Series(
          ["00001", np.nan, "00aaa", np.nan, "45678"],
          dtype=any_string_dtype,
      )
      tm.assert_series_equal(result, expected)
  
imports: from datetime import datetime
  import operator
  import numpy
  import pytest
  from pandas import Series, _testing
label_desc: Use image node_id 20 for calling a global function with example usage: test_zfill(any_string_dtype) without return types