'increment my value by 1
>>> from twisted.trial.test.mockdoctest import Counter
>>> c = Counter(10, 11)
>>> c.incr()
>>> c.value() == 11
True
>>> c.incr()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "twisted/trial/test/mockdoctest.py", line 51, in incr
self.__iadd__(1)
File "twisted/trial/test/mockdoctest.py", line 39, in __iadd__
raise ValueError, "sorry, counter got too big"
ValueError: sorry, counter got too big'

def incr(self):

    self.__iadd__(1)
