def solveans(dat):
    last=dat[0][1]
    ans=L
    for i in range(1,N):
        ans+=abs(last-dat[i][1])
    ans+=dat[i][-1]
    return ans

from collections import defaultdict
import math
T=int(input())
for _ in range(T):
    N,L=map(int,input().split())
    dat=defaultdict(list)
    sl=-(-L//math.sqrt(N))
    for _ in range(N):
        x,y=map(int,input().split())
        dat[(x//sl,y//sl)].append([x,y])
    for k in dat.keys():
        dat[k].sort()
    keys=sorted(dat.keys())
    ans=[]
    for k in keys:
        for d in dat[k]:
            ans.append(d)
    print(len(ans))
    for a,b in ans:
        print(a,b)