code: def test_impulse_invariant(self, sys, sample_time, samples_number):
      time = np.arange(samples_number) * sample_time
      _, yout_cont = impulse2(sys, T=time, **self.tolerances)
      _, yout_disc = dimpulse(
          c2d(sys, sample_time, method="impulse"), n=len(time)
      )
      assert_allclose(
          sample_time * yout_cont.ravel(), yout_disc[0].ravel()
      )
  
imports: import numpy
  from numpy.testing import assert_array_almost_equal, assert_almost_equal, assert_allclose, assert_equal
  import pytest
  from scipy.signal import cont2discrete
  from scipy.signal import dlsim, ss2tf, ss2zpk, lsim2, lti
  from scipy.signal import tf2ss, impulse2, dimpulse, step2, dstep
label_desc: Use image node_id 1 for calling the TestC2dInvariants obj's underlying member method code with example usage: obj.test_impulse_invariant(sys, sample_time, samples_number) without return types