How to reset doctest in jupyter notebook?

Question

I call doctest.testmod() at the end of some my cell to run tests in my notebook.
But when I rerun this cell doctest raise some exception which forces me to restart all notebook.
Is there some function in doctest to reset its internal cache?

Cell[1]:

import doctest

class AttrDict(dict):
    def __getattr__(self, key):
        return self[key]

def foo():
    '''
    >>> foo()
    {}
    '''
    return AttrDict()
doctest.testmod()

Cell[2]:

foo()

Cell[3]:

doctest.testmod()

Cell[3] raises next error:

---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
Cell In[3], line 1
----> 1 doctest.testmod()

File ~/mambaforge/envs/nout/lib/python3.12/doctest.py:1995, in testmod(m, name, globs, verbose, report, optionflags, extraglobs, raise_on_error, exclude_empty)
   1992 else:
   1993     runner = DocTestRunner(verbose=verbose, optionflags=optionflags)
-> 1995 for test in finder.find(m, name, globs=globs, extraglobs=extraglobs):
   1996     runner.run(test)
   1998 if report:

File ~/mambaforge/envs/nout/lib/python3.12/doctest.py:948, in DocTestFinder.find(self, obj, name, module, globs, extraglobs)
    946 # Recursively explore `obj`, extracting DocTests.
    947 tests = []
--> 948 self._find(tests, obj, name, module, source_lines, globs, {})
    949 # Sort the tests by alpha order of names, for consistency in
    950 # verbose-mode output.  This was a feature of doctest in Pythons
    951 # <= 2.3 that got lost by accident in 2.4.  It was repaired in
    952 # 2.4.4 and 2.5.
    953 tests.sort()

File ~/mambaforge/envs/nout/lib/python3.12/doctest.py:1020, in DocTestFinder._find(self, tests, obj, name, module, source_lines, globs, seen)
   1017         valname = '%s.%s' % (name, valname)
   1019         # Recurse to functions & classes.
-> 1020         if ((self._is_routine(val) or inspect.isclass(val)) and
   1021             self._from_module(module, val)):
   1022             self._find(tests, val, valname, module, source_lines,
   1023                        globs, seen)
   1025 # Look for tests in a module's __test__ dictionary.

File ~/mambaforge/envs/nout/lib/python3.12/doctest.py:991, in DocTestFinder._is_routine(self, obj)
    989 maybe_routine = obj
    990 try:
--> 991     maybe_routine = inspect.unwrap(maybe_routine)
    992 except ValueError:
    993     pass

File ~/mambaforge/envs/nout/lib/python3.12/inspect.py:774, in unwrap(func, stop)
    772 memo = {id(f): f}
    773 recursion_limit = sys.getrecursionlimit()
--> 774 while _is_wrapper(func):
    775     func = func.__wrapped__
    776     id_func = id(func)

File ~/mambaforge/envs/nout/lib/python3.12/inspect.py:765, in unwrap.<locals>._is_wrapper(f)
    764 def _is_wrapper(f):
--> 765     return hasattr(f, '__wrapped__')

Cell In[1], line 6, in AttrDict.__getattr__(self, key)
      5 def __getattr__(self, key):
----> 6     return self[key]

KeyError: '__wrapped__'