code: def test_range(self):
      # Test that bode() finds a reasonable frequency range.
      # 1st order low-pass filter: H(s) = 0.3 / (z - 0.2),
      dt = 0.1
      system = TransferFunction(0.3, [1, -0.2], dt=0.1)
      n = 10
      # Expected range is from 0.01 to 10.
      expected_w = np.linspace(0, np.pi, n, endpoint=False) / dt
      w, mag, phase = dbode(system, n=n)
      assert_almost_equal(w, expected_w)
  
imports: from __future__ import division, print_function, absolute_import
  import numpy
  from numpy.testing import assert_equal, assert_array_almost_equal, assert_array_equal, assert_allclose, assert_, assert_almost_equal
  from pytest import raises
  from scipy._lib._numpy_compat import suppress_warnings
  from scipy.signal import dlsim, dstep, dimpulse, tf2zpk, lti, dlti, StateSpace, TransferFunction, ZerosPolesGain, dfreqresp, dbode, BadCoefficients
label_desc: Use image node_id 3 for calling the Test_bode obj's underlying member method code with example usage: obj.test_range() without return types