import sys
input = sys.stdin.readline

T=int(input())
for tests in range(T):
    N,L=map(int,input().split())
    P=[list(map(int,input().split())) for i in range(N)]

    c=L/(N**(1/2))

    LIST=[[] for i in range(int(L/c+3))]

    for x,y in P:
        LIST[int(x/c)].append((x,y))

    ANS=[]

    for i in range(len(LIST)):
        LIST[i].sort()

        if i%2==1:
            LIST[i].reverse()

        for x,y in LIST[i]:
            ANS.append((x,y))

    print(len(ANS)+1)

    for x,y in ANS:
        print(x,y)

    print(*ANS[0])