code: def test_design_matrix(self, xp, scp, dtype):
      if xp.dtype(dtype).kind == "u":
          pytest.skip()
  
      t = xp.arange(-1, 7, dtype=dtype)
      x = xp.arange(1, 5, dtype=dtype)
      k = 2
  
      mat = scp.interpolate.BSpline.design_matrix(x, t, k)
      return mat.todense()
  
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 20 for calling the TestBSpline obj's underlying member method code with example usage: obj.test_design_matrix(xp, scp, dtype) and returns: mat