code: def test_pad(self):
      old = np.array([1, 5, 10], dtype=np.int64)
      new = np.array(list(range(12)), dtype=np.int64)
  
      filler = libalgos.pad["int64_t"](old, new)
  
      expect_filler = np.array(
          [-1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2], dtype=np.intp
      )
      tm.assert_numpy_array_equal(filler, expect_filler)
  
      # corner case
      old = np.array([5, 10], dtype=np.int64)
      new = np.arange(5, dtype=np.int64)
      filler = libalgos.pad["int64_t"](old, new)
      expect_filler = np.array([-1, -1, -1, -1, -1], dtype=np.intp)
      tm.assert_numpy_array_equal(filler, expect_filler)
  
file_path: pandas/pandas/tests/libs/test_libalgos.py
imports: from datetime import datetime
  from itertools import permutations
  import numpy
  from pandas._libs import algos
  import pandas._testing
label_desc: Use image node_id 2 for calling the TestPadBackfill obj's underlying member method code with example usage: obj.test_pad() without return types