def testAdvanceTokenShouldReturnThreeWordWithOneFinalEnd(self):
global tokenzier
tokenizer=Tokenizer('a b c ')
gen=tokenizer.advanceToken()
a=next(gen)
self.assertEqual(a,'a')
b=next(gen)
self.assertEqual(b,'b')
c=next(gen)
self.assertEqual(c,'c')
d=next(gen)
self.assertIsNone(d)
