class_docstr: A class that can be used to replace shap.TreeExplainer so that
  the wrapper can be tested without fitting a model and instantiating
  an actual explainer.
code: def _check_input(self, X):
      if not hasattr(X, "shape"):
          raise TypeError("Input X has no attribute shape!")
  
file_path: alibi/alibi/explainers/tests/utils.py
imports: import numpy
label_desc: Use image node_id 6 for calling the MockTreeExplainer obj's underlying member method code with example usage: obj._check_input(X) without return types