class MealyError(Exception):
    def __init__(self, method_name):
        self.method_name = method_name


class Mealy:
    def __init__(self):
        self.state = 'A'

    def herd(self):
        if self.state == 'A':
            self.state = 'B'
            return 0
        elif self.state == 'B':
            self.state = 'C'
            return 2
        elif self.state == 'D':
            self.state = 'E'
            return 5
        elif self.state == 'E':
            self.state = 'F'
            return 7
        elif self.state == 'F':
            self.state = 'G'
            return 8
        else:
            raise MealyError('herd')

    def stash(self):
        if self.state == 'A':
            self.state = 'C'
            return 1
        elif self.state == 'B':
            self.state = 'G'
            return 3
        elif self.state == 'C':
            self.state = 'D'
            return 4
        elif self.state == 'D':
            self.state = 'G'
            return 6
        elif self.state == 'G':
            self.state = 'C'
            return 9
        else:
            raise MealyError('stash')


def error(func, name):
    try:
        func()
    except MealyError as error:
        assert str(error) == name


def test():
    o = main()
    o.state = "A"
    assert o.herd() == 0
    o.state = "A"
    assert o.stash() == 1
    o.state = "B"
    assert o.herd() == 2
    o.state = "B"
    assert o.stash() == 3
    o.state = "C"
    assert o.stash() == 4
    o.state = "C"
    error(o.herd, "herd")
    o.state = "D"
    assert o.herd() == 5
    o.state = "D"
    assert o.stash() == 6
    o.state = "E"
    assert o.herd() == 7
    o.state = "E"
    error(o.stash, "stash")
    o.state = "F"
    assert o.herd() == 8
    o.state = "F"
    error(o.stash, "stash")
    o.state = "G"
    assert o.stash() == 9
    o.state = "G"
    error(o.stash, "heard")


def main():
    return Mealy()