from math import sqrt
from collections import defaultdict
from operator import itemgetter

def solve():
    N, L = map(int, input().split())

    B = round(L / sqrt(N))
    block = defaultdict(list)

    for i in range(N):
        X, Y = map(int, input().split())

        if Y == 0:
            j = 0
        else:
            j = (Y-1)//B
        block[j].append((X,Y))

    A = []
    for j in sorted(block.keys()):
        if j % 2 == 0:
            block[j].sort(key=itemgetter(0))
        else:
            block[j].sort(key=itemgetter(0), reverse=True)
        A.extend(block[j])

    print(len(A))
    for x,y in A:
        print(x,y)

#==================================================
import sys
input=sys.stdin.readline
write=sys.stdout.write

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