code: def setup_class(cls):
      nsample = 100
      sig = 0.5
      x1 = np.linspace(0, 20, nsample)
      x2 = 5 + 3 * np.random.randn(nsample)
      x = np.c_[
          x1, x2, np.sin(0.5 * x1), (x2 - 5) ** 2, np.ones(nsample)
      ]
      beta = [0.5, 0.5, 1, -0.04, 5.0]
      y_true = np.dot(x, beta)
      y = y_true + sig * np.random.normal(size=nsample)
      exog0 = sm.add_constant(np.c_[x1, x2], prepend=False)
  
      cls.res = sm.OLS(y, exog0).fit()
      cls.res_true = sm.OLS(y, x).fit()
  
imports: import numpy
  from numpy.testing import assert_array_less, assert_equal, assert_raises
  from pandas import DataFrame, Series
  import pytest
  import statsmodels.api
  from statsmodels.graphics.regressionplots import abline_plot, add_lowess, influence_plot, plot_added_variable, plot_ccpr, plot_ccpr_grid, plot_ceres_residuals, plot_fit, plot_leverage_resid2, plot_partial_residuals, plot_partregress_grid, plot_regress_exog
label_desc: Use image node_id 1 for calling the TestPlot obj's underlying member method code with example usage: obj.setup_class(cls) without return types