code: def test_X_dim_fail():
      sr.fit(X[:, :2], y)
      assert_raises(
          ValueError,
          "X must be a 2D array",
          plot_decision_regions,
          X[:, :2].flatten(),
          y,
          sr,
      )
  
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 5 for calling a global function with example usage: test_X_dim_fail() without return types