docstr: Test behavior for signal without local maxima.
docstr_tok: ["Test","behavior","for","signal","without","local","maxima","."]
code: def test_constant(self):
      """
      Test behavior for signal without local maxima.
      """
      open_interval = (None, None)
      peaks, props = find_peaks(
          np.ones(10),
          height=open_interval,
          threshold=open_interval,
          prominence=open_interval,
          width=open_interval,
      )
      assert_(peaks.size == 0)
      for key in self.property_keys:
          assert_(props[key].size == 0)
  
imports: from __future__ import division, print_function, absolute_import
  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._lib.six import xrange
  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 TestFindPeaks obj's underlying member method code with example usage: obj.test_constant() without return types