code: def testBackwardSmoother(self):
      self.dlm1._forwardFilter(start=0, end=19, renew=False)
      self.dlm1.result.filteredSteps = (0, 19)
      self.dlm1._backwardSmoother(start=19)
      self.assertAlmostEqual(
          self.dlm1.result.smoothedObs[0][0, 0], 1.0 / 21
      )
      self.assertAlmostEqual(
          self.dlm1.result.smoothedObs[19][0, 0], 1.0 / 21
      )
  
      self.dlm2._forwardFilter(start=0, end=19)
      self.dlm2.result.filteredSteps = (0, 19)
      self.dlm2._backwardSmoother(start=19)
      self.assertAlmostEqual(self.dlm2.result.smoothedObs[0][0, 0], 0.0)
      self.assertAlmostEqual(
          self.dlm2.result.smoothedObs[19][0, 0], 0.0
      )
      self.assertAlmostEqual(self.dlm2.result.smoothedObs[9][0, 0], 1.0)
  
file_path: pydlm/tests/core/test_dlm.py
imports: from pydlm.modeler.trends import trend
  from pydlm.core._dlm import _dlm
  import logging
  import numpy
  import unittest
label_desc: Use image node_id 6 for calling the test_dlm obj's underlying member method code with example usage: obj.testBackwardSmoother() without return types