code: def test_mean_of_squares():
      """Test _mean_of_squares."""
      n_samples = 11
      n_features = 501  # Higher than 500 required
      signals, _, _ = generate_signals(
          n_features=n_features, length=n_samples, same_variance=True
      )
      # Reference computation
      var1 = np.copy(signals)
      var1 **= 2
      var1 = var1.mean(axis=0)
  
      var2 = nisignal._mean_of_squares(signals)
  
      np.testing.assert_almost_equal(var1, var2)
  
imports: import os.path
  import numpy
  import pytest
  import scipy.signal
  from pandas import read_csv
  from nilearn import signal
  from nilearn.conftest import _rng
  from nilearn.signal import clean
label_desc: Use image node_id 7 for calling a global function with example usage: test_mean_of_squares() without return types