code: def learn(self, obs, label):
      pred_output = self.model.policy(obs)
      mse_loss = paddle.nn.loss.MSELoss()
      cost = mse_loss(pred_output, label)
      cost = paddle.mean(cost)
      return cost
  
imports: import numpy
  import unittest
  import paddle
  import paddle.nn
  import parl
  import os
label_desc: Use image node_id 3 for calling the TestAlgorithm obj's underlying member method code with example usage: obj.learn(obs, label) and returns: cost