def test_1():
it = PeekingIterator(Iterator([1, 2, 3, 4]))
res = []
while it.hasNext():
res.append(it.peek())
res.append(it.next())
assert res == [1, 1, 2, 2, 3, 3, 4, 4]
def test_0():
it = PeekingIterator(Iterator([]))
assert not it.hasNext()