code: def test_invalid_kernel():
      x = np.arange(400)
      y = x**2
      # silverman kernel is not currently in statsmodels kernel library
      with pytest.raises(ValueError):
          nparam.KernelReg(
              x,
              y,
              reg_type="ll",
              var_type="cc",
              bw="cv_ls",
              ckertype="silverman",
          )
  
      with pytest.raises(ValueError):
          nparam.KernelCensoredReg(
              x,
              y,
              reg_type="ll",
              var_type="cc",
              bw="cv_ls",
              censor_val=0,
              ckertype="silverman",
          )
  
imports: import pytest
  import numpy
  import numpy.testing
  import statsmodels.api
label_desc: Use image node_id 2 for calling a global function with example usage: test_invalid_kernel() without return types