docstr: Test if an empty array is returned if no peaks are provided.
code: def test_empty(self):
      """
      Test if an empty array is returned if no peaks are provided.
      """
      out = peak_prominences([1, 2, 3], [])
      for arr, dtype in zip(out, [np.float64, np.intp, np.intp]):
          assert_(arr.size == 0)
          assert_(arr.dtype == dtype)
  
      out = peak_prominences([], [])
      for arr, dtype in zip(out, [np.float64, np.intp, np.intp]):
          assert_(arr.size == 0)
          assert_(arr.dtype == dtype)
  
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 TestPeakProminences obj's underlying member method code with example usage: obj.test_empty() without return types