def merge_sort(data):
    # TODO: Implement me
    pass

"""
Explanation: <small><i>This notebook was prepared by Donne Martin. Source and license info is on GitHub.</i></small>
Challenge Notebook
Problem: Implement merge sort.

Constraints
Test Cases
Algorithm
Code
Unit Test
Solution Notebook

Constraints

Is a naiive solution sufficient?
Yes



Test Cases

Empty input -> []
One element -> [element]
Two or more elements
Left and right subarrays of different lengths

Algorithm
Refer to the Solution Notebook.  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.
Code
End of explanation
"""


# %load test_merge_sort.py
from nose.tools import assert_equal


class TestMergeSort(object):
    def test_merge_sort(self):
        print('Empty input')
        data = []
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, [])

        print('One element')
        data = [5]
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, [5])

        print('Two or more elements')
        data = [5, 1, 7, 2, 6, -3, 5, 7, -1]
        sorted_data = merge_sort(data)
        assert_equal(sorted_data, sorted(data))

        print('Success: test_merge_sort')


def main():
    test = TestMergeSort()
    test.test_merge_sort()


if __name__ == '__main__':
    main()

"""
Explanation: Unit Test
The following unit test is expected to fail until you solve the challenge.
End of explanation
"""


