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))
    
    ans = []
    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)
            ans.append((x, y))
    
    print(len(ans))
    for x, y in ans:
        print(x, y)

    # total = 0
    # for i in range(len(ans)):
    #     total += abs(ans[i][0] - ans[(i + 1) % len(ans)][0])
    #     total += abs(ans[i][1] - ans[(i + 1) % len(ans)][1])
    # print("deb", total < 1000 * L)


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