class_docstr: Splitter that adds the train sets to the test sets.
  
  Takes a splitter ``cv`` and modifies it in the following way:
  The i-th train sets is identical to the i-th train set of ``cv``.
  The i-th test set is the union of the i-th train set and i-th test set of ``cv``.
  
  Parameters
  ----------
  cv : BaseSplitter
      splitter to modify as above
  
  Examples
  --------
  >>> from sktime.datasets import load_airline
  >>> from sktime.split import ExpandingWindowSplitter
  
  >>> y = load_airline()
  >>> y_template = y[:60]
  >>> cv_tpl = ExpandingWindowSplitter(fh=[2, 4], initial_window=24, step_length=12)
  
  >>> splitter = TestPlusTrainSplitter(cv_tpl)
code: def __init__(self, cv):
      self.cv = cv
      super().__init__()
  
      # dispatch split_series to the same split/split_loc as the wrapped cv
      # for performance reasons
      self.clone_tags(cv, "split_series_uses")
  
file_path: sktime/sktime/split/testplustrain.py
imports: from typing import Optional
  import numpy
  import pandas
  from sktime.split.base import BaseSplitter
  from sktime.split.base._common import ACCEPTED_Y_TYPES, SPLIT_GENERATOR_TYPE
label_desc: Use image node_id 1 to create a new TestPlusTrainSplitter object from inherited base classes: BaseSplitter with example: obj = TestPlusTrainSplitter(cv)