argparse.ArgumentError: argument --black: conflicting option string: --black

[jaraco]

After employing the 'allow' technique in the 3.0 release, I merged the changes into jaraco/skeleton and then into irc, but when running the tests, I encountered this error:

Traceback (most recent call last):
  File "/Users/jaraco/code/main/irc/.tox/python/bin/pytest", line 8, in <module>
    sys.exit(console_main())
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/__init__.py", line 180, in console_main
    code = main()
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/__init__.py", line 136, in main
    config = _prepareconfig(args, plugins)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/__init__.py", line 313, in _prepareconfig
    config = pluginmanager.hook.pytest_cmdline_parse(
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/pluggy/hooks.py", line 286, in __call__
    return self._hookexec(self, self.get_hookimpls(), kwargs)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/pluggy/manager.py", line 93, in _hookexec
    return self._inner_hookexec(hook, methods, kwargs)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/pluggy/manager.py", line 84, in <lambda>
    self._inner_hookexec = lambda hook, methods, kwargs: hook.multicall(
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/pluggy/callers.py", line 203, in _multicall
    gen.send(outcome)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/helpconfig.py", line 99, in pytest_cmdline_parse
    config = outcome.get_result()  # type: Config
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/pluggy/callers.py", line 80, in get_result
    raise ex[1].with_traceback(ex[2])
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/pluggy/callers.py", line 187, in _multicall
    res = hook_impl.function(*args)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/__init__.py", line 932, in pytest_cmdline_parse
    self.parse(args)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/__init__.py", line 1204, in parse
    self._preparse(args, addopts=addopts)
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/__init__.py", line 1099, in _preparse
    self.known_args_namespace = ns = self._parser.parse_known_args(
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/argparsing.py", line 147, in parse_known_args
    return self.parse_known_and_unknown_args(args, namespace=namespace)[0]
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/argparsing.py", line 157, in parse_known_and_unknown_args
    optparser = self._getparser()
  File "/Users/jaraco/code/main/irc/.tox/python/lib/python3.8/site-packages/_pytest/config/argparsing.py", line 121, in _getparser
    arggroup.add_argument(*n, **a)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/argparse.py", line 1386, in add_argument
    return self._add_action(action)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/argparse.py", line 1590, in _add_action
    action = super(_ArgumentGroup, self)._add_action(action)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/argparse.py", line 1400, in _add_action
    self._check_conflict(action)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/argparse.py", line 1539, in _check_conflict
    conflict_handler(action, confl_optionals)
  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/argparse.py", line 1548, in _handle_conflict_error
    raise ArgumentError(action, message % conflict_string)
argparse.ArgumentError: argument --black: conflicting option string: --black

I was afraid this might happen. It seems that the order that plugins happen to load can affect the behavior, so if jaraco.test loads first, then pytest-black loads, pytest-black will fail to register its command-line option because jaraco.test already has registered it.