Merge Sort Problem Statement

You are given a sequence of numbers, ARR. Your task is to return a sorted sequence of ARR in non-descending order using the Merge Sort algorithm.

Explanation:

The Merge Sort algorithm is a Divide and Conquer approach. It recursively divides the input array into two halves until the size of each array is 1, then merges the sorted halves to produce a completely sorted array.

Input:

The first line of the input contains an integer ‘T’ representing the number of test cases.
The following 2 * T lines provide the test cases.
For each test case:
- The first line contains an integer ‘N’, representing the number of elements in ‘ARR’.
- The second line contains ‘N’ space-separated integers representing the elements of ‘ARR’. 

Output:

For each test case, return the numbers sorted in non-descending order.

Example:

Input:
T = 1
N = 5
ARR = [3, 1, 4, 1, 5]

Output:
[1, 1, 3, 4, 5]

Constraints:

• 1 <= T <= 50
• 1 <= N <= 10^4
• -10^9 <= arr[i] <= 10^9
• Time Limit: 1 second

Note:

You are not required to print the output; just implement the function as specified by the problem statement.