code: def test_feature_index_fail():
      sr.fit(X, y)
      assert_raises(
          ValueError,
          "Unable to unpack feature_index. Make sure feature_index "
          "only has two dimensions.",
          plot_decision_regions,
          X,
          y,
          sr,
          feature_index=(0, 1, 2),
          filler_feature_values={2: 0.5},
      )
  
file_path: mlxtend/mlxtend/plotting/tests/test_decision_regions.py
imports: import matplotlib.pyplot
  import numpy
  from mlxtend.classifier import SoftmaxRegression
  from mlxtend.data import iris_data
  from mlxtend.plotting import plot_decision_regions
  from mlxtend.utils import assert_raises
label_desc: Use image node_id 4 for calling a global function with example usage: test_feature_index_fail() without return types