code: def test_single_point(self, xp, scp, dim):
      # Make sure interpolation still works with only one point (in 1, 2, and
      # 3 dimensions).
      y = xp.zeros((1, dim))
      d = xp.ones((1,))
      f = self.build(scp, y, d, kernel="linear")(y)
      return d, f
  
imports: import pickle
  import pytest
  import warnings
  import numpy
  from numpy.linalg import LinAlgError
  import cupy
  import cupyx
  from cupy import testing
  import cupyx.scipy.interpolate
  from cupyx.scipy.interpolate._rbfinterp import _AVAILABLE, _SCALE_INVARIANT, _NAME_TO_MIN_DEGREE, NAME_TO_FUNC, _monomial_powers, polynomial_matrix, kernel_matrix
label_desc: Use image node_id 21 for calling the _TestRBFInterpolator obj's underlying member method code with example usage: obj.test_single_point(xp, scp, dim) and returns: d,  f