def test_prefixes(self):
"""Test iterator for letters in a string sequentially."""
prefix = prefixes('vanrossum')
self.assertEqual(next(prefix), '')
self.assertEqual(next(prefix), 'v')
self.assertEqual(next(prefix), 'va')
self.assertEqual(next(prefix), 'van')
self.assertEqual(next(prefix), 'vanr')
self.assertEqual(next(prefix), 'vanro')
self.assertEqual(next(prefix), 'vanros')
self.assertEqual(next(prefix), 'vanross')
self.assertEqual(next(prefix), 'vanrossu')
self.assertEqual(next(prefix), 'vanrossum')
def test_prefixes_produces_an_actual_generator(self):
g = prefixes('ab')
self.assertEqual(g.next(), '')
self.assertEqual(g.next(), 'a')
self.assertEqual(g.next(), 'ab')
self.assertRaises(StopIteration, g.next)
def test_prefixes_produces_prefixes(self):
self.assertEqual(list(prefixes('')), [''])
self.assertEqual(list(prefixes('a')), ['', 'a'])
self.assertEqual(list(prefixes('ab')), ['', 'a', 'ab'])
self.assertEqual(list(prefixes('abc')), ['', 'a', 'ab', 'abc'])
def test_prefixes_produces_an_actual_generator(self):
g = prefixes("ab")
self.assertEqual(g.next(), "")
self.assertEqual(g.next(), "a")
self.assertEqual(g.next(), "ab")
self.assertRaises(StopIteration, g.next)
def test_prefixes_produces_prefixes(self):
self.assertEqual(list(prefixes("")), [""])
self.assertEqual(list(prefixes("a")), ["", "a"])
self.assertEqual(list(prefixes("ab")), ["", "a", "ab"])
self.assertEqual(list(prefixes("abc")), ["", "a", "ab", "abc"])
