import unittest

def merge_sort(arr):

def _merge(left, right):

merged_list = []

i, j = 0, 0

while len(left) > i and len(right) > j:

if left[i] < right[j]:

merged_list.append(left[i])

i += 1

else:

merged_list.append(right[j])

j += 1

while len(left) > i:

merged_list.append(left[i])

i += 1

while len(right) > j:

merged_list.append(right[j])

j += 1

return merged_list

def _merge_sort(list):

if len(list) <= 1:

return list

mid = len(list) // 2

left = _merge_sort(list[:mid])

right = _merge_sort(list[mid:])

return _merge(left, right)

result = _merge_sort(arr)

return result

class TestMergeSort(unittest.TestCase):

def test(self):

arr = merge_sort([5, 3, 2, 1, 4])

self.assertEqual(

arr,

[1, 2, 3, 4, 5]

)

arr = merge_sort([-1, -10, 2, 4, 1])

self.assertEqual(

arr,

[-10, -1, 1, 2, 4]

)

arr = merge_sort([1, -1, 5, 2, 4, 2])

self.assertEqual(

arr,

[-1, 1, 2, 2, 4, 5]

)

arr = merge_sort([5, 2])

self.assertEqual(

arr,

[2, 5]

)

arr = merge_sort([-1, -1, 2, 5, 4, 2])

self.assertEqual(

arr,

[-1, -1, 2, 2, 4, 5]

)

if __name__ == '__main__':

unittest.TestCase()