code: def test_nan(self, xp, scp):
      # nan in, nan out.
      b = scp.interpolate.BSpline.basis_element(
          xp.asarray([0, 1, 1, 2])
      )
      return b(xp.asarray([xp.nan]))
  
imports: import pytest
  import inspect
  from cupy import testing
  from cupy_backends.cuda.api import driver
  from cupy_backends.cuda.api import runtime
  import numpy
  import cupyx.scipy.interpolate
label_desc: Use image node_id 19 for calling the TestBSpline obj's underlying member method code with example usage: obj.test_nan(xp, scp) and returns: b