Write a function to sort the given array by using merge sort.
def merge(a,b):
    c = []
    while len(a) != 0 and len(b) != 0:
        if a[0] < b[0]:
            c.append(a[0])
            a.remove(a[0])
        else:
            c.append(b[0])
            b.remove(b[0])
    if len(a) == 0:
        c += b
    else:
        c += a
    return c
def merge_sort(x):
    if len(x) == 0 or len(x) == 1:
        return x
    else:
        middle = len(x)//2
        a = merge_sort(x[:middle])
        b = merge_sort(x[middle:])
        return merge(a,b)

<s>[INST]<<SYS>>Given a task and its code, generate test cases for the code.<</SYS>>Write a function to sort the given array by using merge sort.
def merge(a,b):
    c = []
    while len(a) != 0 and len(b) != 0:
        if a[0] < b[0]:
            c.append(a[0])
            a.remove(a[0])
        else:
            c.append(b[0])
            b.remove(b[0])
    if len(a) == 0:
        c += b
    else:
        c += a
    return c
def merge_sort(x):
    if len(x) == 0 or len(x) == 1:
        return x
    else:
        middle = len(x)//2
        a = merge_sort(x[:middle])
        b = merge_sort(x[middle:])
        return merge(a,b)
[/INST]assert merge_sort([3, 4, 2, 6, 5, 7, 1, 9]) == [1, 2, 3, 4, 5, 6, 7, 9]
assert merge_sort([7, 25, 45, 78, 11, 33, 19]) == [7, 11, 19, 25, 33, 45, 78]
assert merge_sort([3, 1, 4, 9, 8]) == [1, 3, 4, 8, 9]</s>