code: def testBackwardSmoother(self):
      dlm = builder()
      dlm.add(self.trend0)
      dlm.initialize()
  
      # with mean being 0 and observe 1 and 0 consectively, one shall
      # expect the smoothed mean at 1 will be 1/3, for discount = 1
      self.kf1.forwardFilter(dlm.model, 1)
      self.kf1.forwardFilter(dlm.model, 0)
      self.kf1.backwardSmoother(
          dlm.model, np.matrix([[0.5]]), np.matrix([[0.375]])
      )
      self.assertAlmostEqual(dlm.model.obs[0, 0], 1.0 / 3)
      self.assertAlmostEqual(dlm.model.sysVar[0, 0], 0.18518519)
  
file_path: pydlm/tests/base/testKalmanFilter.py
imports: import numpy
  import unittest
  from pydlm.modeler.trends import trend
  from pydlm.modeler.seasonality import seasonality
  from pydlm.modeler.builder import builder
  from pydlm.base.kalmanFilter import kalmanFilter
label_desc: Use image node_id 4 for calling the testKalmanFilter obj's underlying member method code with example usage: obj.testBackwardSmoother() without return types