def test_replace(self, size):
        replacement = 'a'
        s = ' ' * size
        s = s.replace(' ', replacement)
        self.assertEquals(len(s), size)
        self.assertEquals(s.count(replacement), size)
        s = s.replace(replacement, ' ', size - 4)
        self.assertEquals(len(s), size)
        self.assertEquals(s.count(replacement), 4)
        self.assertEquals(s[-10:], '      aaaa')