code: def test_full_index_is_fitted():
      """[Base] FoldIndex: check fit methods."""
      idx = FoldIndex(4)
      assert not idx.n_samples
      idx.fit(X)
      assert idx.n_samples
  
      idx = FoldIndex(4)
      assert not idx.n_samples
      for _ in idx.generate(X):
          pass
      assert idx.n_samples
  
      idx = FoldIndex(4, X)
      assert idx.n_samples
  
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 6 for calling a global function with example usage: test_full_index_is_fitted() without return types