MNT test_tree.py::test_diabetes_underfit is flaky: it fails when changing the random seed #32192
Description
Describe the bug
test_tree.py::test_diabetes_underfit is flaky: it fails when changing the random seed.
I will open a PR to fix it.
Steps/Code to Reproduce
Change the random seed in sklearn/tree/tests/test_tree.py::test_diabetes_underfit and run it with pytest. Almost any other seed will make at least one of the 8 generated tests (by @pytest.mark.parametrize) break.
Expected Results
Test passes for any random seed (or at least for ~99.9% of them).
Actual Results
Tests break, with for instance:
FAILED sklearn/tree/tests/test_tree.py::test_diabetes_underfit[friedman_mse-15-mean_squared_error-60-ExtraTreeRegressor-ExtraTreeRegressor] - assert 343.3070340521192 < 60
Or:
FAILED sklearn/tree/tests/test_tree.py::test_diabetes_underfit[absolute_error-20-mean_squared_error-60-ExtraTreeRegressor-ExtraTreeRegressor] - assert 0 < 0.0
Versions
System:
python: 3.12.11 (main, Aug 18 2025, 19:19:11) [Clang 20.1.4 ]
executable: /home/arthur/dev-perso/scikit-learn/sklearn-env/bin/python
machine: Linux-6.14.0-29-generic-x86_64-with-glibc2.39
Python dependencies:
sklearn: 1.8.dev0
pip: None
setuptools: 80.9.0
numpy: 2.3.3
scipy: 1.16.2
Cython: 3.1.3
pandas: 2.3.2
matplotlib: 3.10.6
joblib: 1.5.2
threadpoolctl: 3.6.0
Built with OpenMP: True
threadpoolctl info:
user_api: blas
internal_api: openblas
num_threads: 16
prefix: libscipy_openblas
filepath: /home/arthur/dev-perso/scikit-learn/sklearn-env/lib/python3.12/site-packages/numpy.libs/libscipy_openblas64_-8fb3d286.so
version: 0.3.30
threading_layer: pthreads
architecture: Haswell
user_api: blas
internal_api: openblas
num_threads: 16
prefix: libscipy_openblas
filepath: /home/arthur/dev-perso/scikit-learn/sklearn-env/lib/python3.12/site-packages/scipy.libs/libscipy_openblas-b75cc656.so
version: 0.3.29.dev
threading_layer: pthreads
architecture: Haswell
user_api: openmp
internal_api: openmp
num_threads: 16
prefix: libgomp
filepath: /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0
version: None