docstr: Test with empty signal.
code: def test_empty(self):
      """Test with empty signal."""
      x = np.array([], dtype=np.float64)
      for array in _local_maxima_1d(x):
          assert_equal(array, np.array([]))
          assert_(array.base is None)
  
imports: import copy
  import numpy
  from numpy.testing import assert_, assert_equal, assert_allclose, assert_array_equal
  import pytest
  from pytest import raises, warns
  from scipy.signal._peak_finding import argrelmax, argrelmin, peak_prominences, peak_widths, _unpack_condition_args, find_peaks, find_peaks_cwt, _identify_ridge_lines
  from scipy.signal._peak_finding_utils import _local_maxima_1d, PeakPropertyWarning
label_desc: Use image node_id 1 for calling the TestLocalMaxima1d obj's underlying member method code with example usage: obj.test_empty() without return types