code: def test_formula():
      y, x, w = gen_data(250, 3, True, pandas=True)
      fmla = "y ~ 1 + x0 + x1 + x2"
      data = pd.concat([y, x], axis=1)
      mod = RollingWLS.from_formula(
          fmla, window=100, data=data, weights=w
      )
      res = mod.fit()
      alt = RollingWLS(y, x, window=100)
      alt_res = alt.fit()
      assert_allclose(res.params, alt_res.params)
      ols_mod = RollingOLS.from_formula(fmla, window=100, data=data)
      ols_mod.fit()
  
imports: from io import BytesIO
  from itertools import product
  import warnings
  import numpy
  import pandas
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal
  from statsmodels import tools
  from statsmodels.regression.linear_model import WLS
  from statsmodels.regression.rolling import RollingWLS, RollingOLS
label_desc: Use image node_id 13 for calling a global function with example usage: test_formula() without return types