import sys
input = sys.stdin.readline

T=int(input())

for _ in range(T):
    N,L=map(int,input().split())
    XY=[list(map(int,input().split())) for _ in range(N)]
    rtL = int(L**0.5)+1
    divXY = [[] for _ in range(L//rtL+1)]
    for x,y in XY:
        divXY[y//rtL].append((x,y))
    ans = []
    for i,div in enumerate(divXY):
        div.sort()
        if i%2==0:
            ans.extend(div)
        else:
            ans.extend(div[::-1])
    print(len(ans))
    for x,y in ans:
        print(x,y)