code: def test_forward(self):
      batch_size = (3, 2, 4)
      x1 = torch.randn(*batch_size, 7, 9)
      x2 = torch.randn(*batch_size, 6, 9)
      # Doesn't support ARD
      lengthscale = (
          torch.randn(*batch_size).view(*batch_size, 1, 1) ** 2
      )
      res = gpytorch.functions.RBFCovariance.apply(
          x1, x2, lengthscale, sq_dist_func
      )
      actual = sq_dist_func(x1, x2).div(-2 * lengthscale**2).exp()
      self.assertTrue(torch.allclose(res, actual))
  
imports: import unittest
  import torch
  import gpytorch
label_desc: Use image node_id 1 for calling the TestRBFCovariance obj's underlying member method code with example usage: obj.test_forward() without return types