code: def setup_class(cls):
      nobs = 200
      # x = np.arange(nobs*3).reshape(nobs,-1)
      np.random.seed(187678)
      x = np.random.randn(nobs, 3)
  
      xk = np.array([1, 2, 3])
      xk = np.array([1.0, 1.0, 1.0])
      # xk = np.zeros(3)
      beta = xk
      y = np.dot(x, beta) + 0.1 * np.random.randn(nobs)
      xkols = np.dot(np.linalg.pinv(x), y)
  
      cls.x = x
      cls.y = y
      cls.params = [np.array([1.0, 1.0, 1.0]), xkols]
      cls.init()
  
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 CheckDerivativeMixin obj's underlying member method code with example usage: obj.setup_class(cls) without return types