import re
import threading


def ins1(b, l):
    b.wait()
    l.insert(0, 'potato')

def get_secret(b, l):
    b.wait()
    assert l[-1] != 'super secret password'


def check(funcs, *args):
    barrier = threading.Barrier(len(funcs))
    thrds = []

    for func in funcs:
        thrd = threading.Thread(target=func, args=(barrier, *args))

        thrds.append(thrd)
        thrd.start()

    for thrd in thrds:
        thrd.join()


if __name__ == "__main__":
    while True:
        check([ins1] + [get_secret] * 10, ['super secret password', 'tomato'])

$ ./python ../check.py 
Exception in thread Thread-38474 (get_secret):
Traceback (most recent call last):
  File "/home/tom/work/cpython/free/cp/Lib/threading.py", line 1054, in _bootstrap_inner
    self.run()
    ~~~~~~~~^^
  File "/home/tom/work/cpython/free/cp/Lib/threading.py", line 996, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/tom/work/cpython/free/cp/../check.py", line 11, in get_secret
    assert l[-1] != 'super secret password'
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError