code: def test_dstep_4(self):
      # Raise an error for continuous-time systems
      system = signal.lti([1], [1, 1])
      with assert_raises(AttributeError):
          signal.dstep(system)
  
imports: from math import sqrt, pi
  from pytest import raises
  import cupy
  from cupy import testing
  import cupyx.scipy.signal
label_desc: Use image node_id 11 for calling the TestDLTI obj's underlying member method code with example usage: obj.test_dstep_4() without return types