code: def test_array_mean_centering():
      X1 = np.array([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]])
      X1_out = np.array([[-1.0, -1.0, -1.0], [1.0, 1.0, 1.0]])
      mc = MeanCenterer()
      assert mc.fit_transform(X1).all() == X1_out.all()
  
imports: import numpy
  import pytest
  from mlxtend.preprocessing import MeanCenterer
label_desc: Use image node_id 2 for calling a global function with example usage: test_array_mean_centering() without return types