code: def test_matthews_corr_coef():
      y_targ = [1, 1, 1, 0, 0, 1, 0, 1]
      y_pred = [1, 0, 1, 0, 0, 0, 1, 1]
      res = scoring(
          y_target=y_targ,
          y_predicted=y_pred,
          metric="matthews_corr_coef",
      )
      assert round(res, 3) == 0.258, res
  
file_path: mlxtend/mlxtend/evaluate/tests/test_scoring.py
imports: import numpy
  from mlxtend.evaluate import scoring
label_desc: Use image node_id 13 for calling a global function with example usage: test_matthews_corr_coef() without return types