code: def test_OLS_degenerate(X, Y):
      X[:, 0] = X[:, 1] + X[:, 2]
      model = OLSModel(design=X)
      results = model.fit(Y)
      assert results.df_residuals == 31
  
file_path: nilearn/nilearn/glm/tests/test_regression.py
imports: import pytest
  from numpy.testing import assert_almost_equal, assert_array_almost_equal, assert_array_equal
  from nilearn.glm import ARModel, OLSModel, SimpleRegressionResults
label_desc: Use image node_id 7 for calling a global function with example usage: test_OLS_degenerate(X, Y) without return types