code: def setUp(self):
      self.prev_type = torch.get_default_dtype()
      torch.set_default_dtype(torch.float64)
  
imports: import unittest
  import torch
  from linear_operator.operators import CholLinearOperator, TriangularLinearOperator
  import gpytorch
  from gpytorch.constraints import GreaterThan
  from gpytorch.distributions import MultivariateNormal
  from gpytorch.variational import NaturalVariationalDistribution, TrilNaturalVariationalDistribution
label_desc: Use image node_id 1 for calling the Float64Test obj's underlying member method code with example usage: obj.setUp() without return types