An error in the gmpy2 test suite was reported at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=960201
 
The test suite is run using doctest and has been running without issues for many years. The first failure occurs when running the following fragment:

>>> x = xmpz(16)
>>> iter = x.iter_bits()
>>> [b for b in iter]
[False, False, False, False, True]

The output is as expected when run interactively on 3.8.3rc1 but generated the following error message:

/home/case/local/lib/python3.8/doctest.py:1336: RuntimeWarning: coroutine '<module>' was never awaited
  exec(compile(example.source, filename, "single",
RuntimeWarning: Enable tracemalloc to get the object allocation traceback
**********************************************************************
File "test_gmpy2_xmpz_misc.txt", line 91, in test_gmpy2_xmpz_misc.txt
Failed example:
    [b for b in iter]
Differences (ndiff with -expected +actual):
    - [False, False, False, False, True]
**********************************************************************

Note the runtime warning for doctest.py.