def test_example2():
digits = [1, 0, 9, 9]
assert ([1, 1, 0, 0] == plus_one(digits))
def test_example1():
digits = [1, 2, 3]
assert ([1, 2, 4] == plus_one(digits))
def test_case2():
digits = [1, 9, 9]
assert ([2, 0, 0] == plus_one(digits))
def test_case3():
digits = [9]
assert ([1, 0] == plus_one(digits))
def test_case1():
digits = [9, 9]
assert ([1, 0, 0] == plus_one(digits))
