mock for subprocess run

# allows you to say with mock_run(...):
#   ....
# good for testing scripts that do a lot of subprocess.run calls

class CmdMatch(NamedTuple):
    cmd: str
    matches: str = ".*"
    result: str = ""
    side_effect: Union[Callable, Exception] = None


@contextlib.contextmanager
def mock_run(*cmd_match: Union[str, CmdMatch], **kws):
    sub_run = subprocess.run
    mock = MagicMock()
    if isinstance(cmd_match[0], str):
        cmd_match = [CmdMatch(*cmd_match, **kws)]

    def new_run(cmd, **_kws):
        check_cmd = " ".join(cmd[1:])
        mock(*cmd[1:])
        for m in cmd_match:
            if m.cmd in cmd[0].lower() and re.match(m.matches, check_cmd):
                if m.side_effect:
                    if isinstance(m.side_effect, Exception):
                        raise m.side_effect
                    m.side_effect()
                return subprocess.CompletedProcess(cmd, 0, m.result, "")
        assert False, "No matching call for %s" % check_cmd

    subprocess.run = new_run
    yield mock
    subprocess.run = sub_run