new_contents: import torch
  from gpytorch.utils.interpolation import Interpolation
  from gpytorch import utils
  
  
  def test_interpolation():
      x = torch.linspace(0.01, 1, 100)
      grid = torch.linspace(-0.05, 1.05, 50)
      J, C = Interpolation().interpolate(grid, x)
      W = utils.index_coef_to_sparse(J, C, len(grid))
      test_func_grid = grid.pow(2)
      test_func_x = x.pow(2)
  
      interp_func_x = torch.dsmm(W, test_func_grid.unsqueeze(1)).squeeze()
  
      assert all(torch.abs(interp_func_x - test_func_x) / (test_func_x + 1e-10) < 1e-5)
  
subject: Add basic unit test for cubic interpolation