from math import sqrt


def solve():
    N, L = map(int, input().split())
    C = max(1, (int(sqrt(2 * (L * L) // N))))
    ls = [[] for _ in range(L // C + 2)]

    for _ in range(N):
        x, y = map(int, input().split())
        ls[y // C].append((x, y))
    
    for i in range(L // C + 2):
        if len(ls[i]) == 0:
            continue
        ls[i].sort()
        for x, y in ls[i]:
            print(x, y)
    


T = int(input())
for _ in range(T):
    solve()