code: def test_symmetry(self):
      pen = self.pen
      x = self.params
  
      p = np.array([pen.func(np.atleast_1d(xi)) for xi in x])
      assert_allclose(p, p[::-1], rtol=1e-10)
      # func(0) should be 0
      assert_allclose(pen.func(0 * np.atleast_1d(x[0])), 0, rtol=1e-10)
  
imports: import numpy
  from numpy.testing import assert_allclose, assert_equal
  import statsmodels.base._penalties
  from statsmodels.tools.numdiff import approx_fprime, approx_hess
label_desc: Use image node_id 1 for calling the CheckPenalty obj's underlying member method code with example usage: obj.test_symmetry() without return types