code: def test_full_raises_on_empty():
      """[Base] FoldIndex: check raises error on singular array."""
      with np.testing.assert_raises(ValueError):
          FoldIndex(2, np.empty(1))
  
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 13 for calling a global function with example usage: test_full_raises_on_empty() without return types