code: def testFitBackwardSmoother(self):
      self.dlm1.fitForwardFilter()
      self.dlm1.fitBackwardSmoother()
      self.assertEqual(self.dlm1.result.smoothedSteps, [0, 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.fitForwardFilter()
      self.dlm2.fitBackwardSmoother()
      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)
  
imports: import numpy
  import unittest
  from pydlm.modeler.trends import trend
  from pydlm.modeler.seasonality import seasonality
  from pydlm.modeler.dynamic import dynamic
  from pydlm.modeler.autoReg import autoReg
  from pydlm.dlm import dlm
label_desc: Use image node_id 5 for calling the testDlm obj's underlying member method code with example usage: obj.testFitBackwardSmoother() without return types