def test_normal_peek():
"""Test flatten with peeking at iterable."""
# flatten two iterables
data1, data2 = iter('ABC'), iter('DEF')
lst = (x for x in (data1, data2))
res = flatten(lst)
assert next(res) == 'A'
assert next(data1)
assert list(res) == ['C', 'D', 'E', 'F']
assert list(lst) == []
assert list(data1) == []
assert list(data2) == []
# flatten one iterable
data = iter('ABC')
lst = (x for x in (data,))
res = flatten(lst)
assert next(res) == 'A'
assert next(data) == 'B'
assert list(res) == ['C']
assert list(lst) == []
assert list(data) == []
# flatten two iterables, one empty
data1, data2 = iter('ABC'), ()
lst = (x for x in (data1, data2))
res = flatten(lst)
assert next(res) == 'A'
assert next(data1) == 'B'
assert list(res) == ['C']
assert list(lst) == []
assert list(data1) == []
# flatten two iterables, one empty
data1, data2 = (), iter('DEF')
lst = (x for x in (data1, data2))
res = flatten(lst)
assert next(res) == 'D'
assert next(data2) == 'E'
assert list(res) == ['F']
assert list(lst) == []
assert list(data2) == []
def test_normal():
"""Test flatten."""
# flatten two iterables
data1, data2 = iter('ABC'), iter('DEF')
lst = (x for x in (data1, data2))
res = flatten(lst)
assert next(res) == 'A'
assert list(res) == ['B', 'C', 'D', 'E', 'F']
assert list(lst) == []
assert list(data1) == []
assert list(data2) == []
# flatten one iterable
data = iter('ABC')
lst = (x for x in (data,))
res = flatten(lst)
assert next(res) == 'A'
assert list(res) == ['B', 'C']
assert list(lst) == []
assert list(data) == []
# flatten two iterables, one empty
data1, data2 = iter('ABC'), ()
lst = (x for x in (data1, data2))
res = flatten(lst)
assert next(res) == 'A'
assert list(res) == ['B', 'C']
assert list(lst) == []
assert list(data1) == []
# flatten two iterables, one empty
data1, data2 = (), iter('DEF')
lst = (x for x in (data1, data2))
res = flatten(lst)
assert next(res) == 'D'
assert list(res) == ['E', 'F']
assert list(lst) == []
assert list(data2) == []
# flatten two iterables, both empty
data1, data2 = (), ()
lst = (x for x in (data1, data2))
res = flatten(lst)
assert list(res) == []
assert list(lst) == []
# flatten one iterable, empty
data = ()
lst = (x for x in (data,))
res = flatten(lst)
assert list(res) == []
assert list(lst) == []