class_docstr: The GetFunctionTestCase class can be imported and used to test foreign
  implementations of the `get` function specification. It aims to enforce all
  known expectations of `get` functions.
  
  To use the class, inherit from it and override the `get` function. For
  example:
  
  > from dask.utils_test import GetFunctionTestMixin
  > class TestCustomGet(GetFunctionTestMixin):
       get = staticmethod(myget)
  
  Note that the foreign `myget` function has to be explicitly decorated as a
  staticmethod.
code: def test_badkey(self):
      d = {":x": 1, ":y": (inc, ":x"), ":z": (add, ":x", ":y")}
      try:
          result = self.get(d, "badkey")
      except KeyError:
          pass
      else:
          msg = "Expected `{}` with badkey to raise KeyError.\n"
          msg += f"Obtained '{result}' instead."
          assert False, msg.format(self.get.__name__)
  
imports: from __future__ import annotations
  import contextlib
  import importlib
  import time
  from typing import TYPE_CHECKING
label_desc: Use image node_id 2 for calling the GetFunctionTestMixin obj's underlying member method code with example usage: obj.test_badkey() without return types