code: def test_initialize(self):
      kernel_1 = RBFKernel().initialize(lengthscale=1)
      kernel_2 = RBFKernel().initialize(lengthscale=2)
      kernel_add = kernel_1 + kernel_2
      d = {"kernels.0.lengthscale": 0.0, "kernels.1.lengthscale": 5.0}
      kernel_add.initialize(**d)
      self.assertEqual(kernel_add.kernels[0].lengthscale, 0.0)
      self.assertEqual(kernel_add.kernels[1].lengthscale, 5.0)
  
imports: import math
  import unittest
  import linear_operator
  import torch
  import gpytorch
  from gpytorch.kernels import LinearKernel, MaternKernel, RBFKernel, RFFKernel
label_desc: Use image node_id 17 for calling the TestAdditiveAndProductKernel obj's underlying member method code with example usage: obj.test_initialize() without return types