def max_number(arr, k):
    arr.sort(reverse=True)
    n = len(arr)
    for _ in range(k):
        arr[-2] = str(arr[-2]) + str(arr[-1])
        arr.pop()
    return int(arr[-1])

t = int(input())
for _ in range(t):
    n, k = map(int, input().split())
    arr = list(map(int, input().split()))
    print(max_number(arr, k))