code: def test_blend_raises_empty_test():
      """[Base] BlendIndex: check raises error on empty test set."""
      with np.testing.assert_raises(ValueError):
          BlendIndex(0, 10, X=X)
  
imports: import os
  import subprocess
  import numpy
  from mlens import config
  from mlens.utils import IdTrain
  from mlens.index import FoldIndex, BlendIndex, SubsetIndex, TemporalIndex, ClusteredSubsetIndex, FullIndex
  from mlens.index.base import partition, prune_train
label_desc: Use image node_id 27 for calling a global function with example usage: test_blend_raises_empty_test() without return types