code: def setup_class(cls):
      super().setup_class()
      xkols = np.dot(np.linalg.pinv(cls.x), cls.y)
      cls.params = [np.array([1.0, 1.0, 1.0]), xkols]
      cls.args = (cls.x,)
  
imports: import numpy
  from numpy.testing import assert_allclose, assert_almost_equal
  import statsmodels.api
  from statsmodels.tools import numdiff
  from statsmodels.tools.numdiff import approx_fprime, approx_fprime_cs, approx_hess_cs, _approx_fprime_scalar, _approx_fprime_cs_scalar
label_desc: Use image node_id 1 for calling the TestDerivativeFun obj's underlying member method code with example usage: obj.setup_class(cls) without return types